diff --git a/lib/primitives/mtx.js b/lib/primitives/mtx.js
index d6d19c5b..7ac33f9b 100644
--- a/lib/primitives/mtx.js
+++ b/lib/primitives/mtx.js
@@ -947,7 +947,7 @@ MTX.prototype.isInputScripted = function isInputScripted(index) {
 
 /**
  * Estimate maximum possible size.
- * @param {(Wallet|Object)?} options - Wallet or options object.
+ * @param {Object?} options - Wallet or options object.
  * @param {Number} options.m - Multisig `m` value.
  * @param {Number} options.n - Multisig `n` value.
  * @returns {Number}
@@ -1069,7 +1069,7 @@ MTX.prototype.maxSize = function maxSize(options) {
       // simply add more of the fee to the change
       // output.
       // m value
-      m = options.m || 3;
+      m = options.m || 2;
       // n value
       n = options.n || 3;
       // OP_0
@@ -1144,7 +1144,8 @@ MTX.prototype._guessRedeem = function guessRedeem(options, hash) {
  * See {@link TX#getMinFee} vs. {@link TX#getRoundFee}.
  * @param {Boolean} options.free - Do not apply a fee if the
  * transaction priority is high enough to be considered free.
- * @param {Amount?} options.fee - Use a hard fee rather than calculating one.
+ * @param {Amount?} options.hardFee - Use a hard fee rather
+ * than calculating one.
  * @param {Rate?} options.rate - Rate used for fee calculation.
  * @param {Number|Boolean} options.subtractFee - Whether to subtract the
  * fee from * existing outputs rather than adding more inputs.
@@ -1154,155 +1155,8 @@ MTX.prototype._guessRedeem = function guessRedeem(options, hash) {
  */
 
 MTX.prototype.selectCoins = function selectCoins(coins, options) {
-  var chosen = [];
-  var index = 0;
-  var tx = this.clone();
-  var outputValue = tx.getOutputValue();
-  var tryFree, size, change, fee;
-
-  if (!options)
-    options = {};
-
-  tryFree = options.free;
-
-  // Null the inputs if there are any.
-  tx.inputs.length = 0;
-
-  if (!options.selection || options.selection === 'age') {
-    // Oldest unspents first
-    coins = coins.slice().sort(function(a, b) {
-      a = a.height === -1 ? 0x7fffffff : a.height;
-      b = b.height === -1 ? 0x7fffffff : b.height;
-      return a - b;
-    });
-  } else if (options.selection === 'random' || options.selection === 'all') {
-    // Random unspents
-    coins = coins.slice().sort(function() {
-      return Math.random() > 0.5 ? 1 : -1;
-    });
-  }
-
-  function total() {
-    if (options.subtractFee || options.subtractFee === 0)
-      return outputValue;
-    return outputValue + fee;
-  }
-
-  function isFull() {
-    return tx.getInputValue() >= total();
-  }
-
-  function addCoins() {
-    var coin;
-
-    while (index < coins.length) {
-      coin = coins[index++];
-
-      if (options.confirmed && coin.height === -1)
-        continue;
-
-      if (options.height >= 0 && coin.coinbase) {
-        if (options.height + 1 < coin.height + constants.tx.COINBASE_MATURITY)
-          continue;
-      }
-
-      // Add new inputs until TX will have enough
-      // funds to cover both minimum post cost
-      // and fee.
-      tx.addInput(coin);
-      chosen.push(coin);
-
-      if (options.selection === 'all')
-        continue;
-
-      // Stop once we're full.
-      if (isFull())
-        break;
-    }
-  }
-
-  if (options.fee != null) {
-    fee = options.fee;
-
-    if (fee > constants.tx.MAX_FEE)
-      fee = constants.tx.MAX_FEE;
-
-    // Transfer `total` funds maximum.
-    addCoins();
-  } else {
-    fee = constants.tx.MIN_FEE;
-
-    // Transfer `total` funds maximum.
-    addCoins();
-
-    // Add dummy output (for `change`) to
-    // calculate maximum TX size.
-    tx.addOutput({
-      // In case we don't have a change address,
-      // use a fake p2pkh output to gauge size.
-      script: options.changeAddress
-        ? Script.fromAddress(options.changeAddress)
-        : Script.fromPubkeyhash(constants.ZERO_HASH160),
-      value: 0
-    });
-
-    // Change fee value if it is more than 1024
-    // bytes (10000 satoshi for every 1024 bytes).
-    do {
-      // Calculate max possible size after signing.
-      size = tx.maxSize(options);
-
-      if (tryFree && options.height >= 0) {
-        // Note that this will only work
-        // if the mempool's rolling reject
-        // fee is zero (i.e. the mempool is
-        // not full).
-        if (tx.isFree(options.height + 1, size)) {
-          fee = 0;
-          break;
-        }
-        tryFree = false;
-      }
-
-      if (options.round)
-        fee = tx.getRoundFee(size, options.rate);
-      else
-        fee = tx.getMinFee(size, options.rate);
-
-      if (fee > constants.tx.MAX_FEE)
-        fee = constants.tx.MAX_FEE;
-
-      if (options.maxFee && fee > options.maxFee) {
-        throw new FundingError(
-          'Fee is too high.',
-          tx.getInputValue(),
-          total());
-      }
-
-      // Failed to get enough funds, add more coins.
-      if (!isFull())
-        addCoins();
-    } while (!isFull() && index < coins.length);
-  }
-
-  if (!isFull()) {
-    // Still failing to get enough funds.
-    throw new FundingError(
-      'Not enough funds.',
-      tx.getInputValue(),
-      total());
-  }
-
-  // How much money is left after filling outputs.
-  change = tx.getInputValue() - total();
-
-  // Return necessary inputs and change.
-  return {
-    coins: chosen,
-    change: change,
-    fee: fee,
-    total: total()
-  };
+  var selector = new CoinSelector(this, options);
+  return selector.select(coins);
 };
 
 /**
@@ -1370,27 +1224,24 @@ MTX.prototype.subtractFee = function subtractFee(fee, index) {
  * Select coins and fill the inputs.
  * @param {Coin[]} coins
  * @param {Object} options - See {@link MTX#selectCoins} options.
- * @returns {Object} See {@link MTX#selectCoins} return value.
+ * @returns {CoinSelector}
  */
 
 MTX.prototype.fund = function fund(coins, options) {
-  var result, i, change, changeAddress;
+  var i, result, change, changeAddress;
 
   assert(this.inputs.length === 0, 'TX is already filled.');
 
-  if (!options)
-    options = {};
-
   // Select necessary coins.
   result = this.selectCoins(coins, options);
 
   // We need a change address.
-  changeAddress = options.changeAddress;
+  changeAddress = result.changeAddress;
 
   // If change address is not available,
   // send back to one of the coins' addresses.
-  for (i = 0; i < result.coins.length && !changeAddress; i++)
-    changeAddress = result.coins[i].getAddress();
+  for (i = 0; i < result.chosen.length && !changeAddress; i++)
+    changeAddress = result.chosen[i].getAddress();
 
   // Will only happen in rare cases where
   // we're redeeming all non-standard coins.
@@ -1398,12 +1249,12 @@ MTX.prototype.fund = function fund(coins, options) {
     throw new Error('No change address available.');
 
   // Add coins to transaction.
-  for (i = 0; i < result.coins.length; i++)
-    this.addInput(result.coins[i]);
+  for (i = 0; i < result.chosen.length; i++)
+    this.addInput(result.chosen[i]);
 
   // Attempt to subtract fee.
-  if (options.subtractFee || options.subtractFee === 0)
-    this.subtractFee(result.fee, options.subtractFee);
+  if (result.shouldSubtract)
+    this.subtractFee(result.fee, result.subtractFee);
 
   // Add a change output.
   this.addOutput({
@@ -1439,21 +1290,8 @@ MTX.prototype.sortMembers = function sortMembers() {
     assert(changeOutput);
   }
 
-  this.inputs = this.inputs.slice().sort(function(a, b) {
-    var h1 = new Buffer(a.prevout.hash, 'hex');
-    var h2 = new Buffer(b.prevout.hash, 'hex');
-    var res = utils.cmp(h1, h2);
-    if (res !== 0)
-      return res;
-    return a.prevout.index - b.prevout.index;
-  });
-
-  this.outputs = this.outputs.slice().sort(function(a, b) {
-    var res = a.value - b.value;
-    if (res !== 0)
-      return res;
-    return utils.cmp(a.script.toRaw(), b.script.toRaw());
-  });
+  this.inputs.sort(sortInputs);
+  this.outputs.sort(sortOutputs);
 
   if (this.changeIndex !== -1) {
     this.changeIndex = this.outputs.indexOf(changeOutput);
@@ -1591,6 +1429,306 @@ MTX.isMTX = function isMTX(obj) {
     && typeof obj.scriptInput === 'function';
 };
 
+/**
+ * Coin Selector
+ * @constructor
+ * @param {TX} tx
+ * @param {Object?} options
+ */
+
+function CoinSelector(tx, options) {
+  if (!(this instanceof CoinSelector))
+    return new CoinSelector(tx, options);
+
+  if (!options)
+    options = {};
+
+  this.tx = tx.clone();
+  this.coins = [];
+  this.outputValue = -1;
+  this.index = -1;
+  this.chosen = [];
+  this.change = -1;
+  this.fee = -1;
+
+  this.type = options.selection || 'age';
+  this.shouldSubtract = !!options.subtractFee || options.subtractFee === 0;
+  this.free = options.free || false;
+  this.subtractFee = options.subtractFee || null;
+  this.height = options.height || -1;
+  this.confirmations = options.confirmations || -1;
+  this.hardFee = options.hardFee || null;
+  this.changeAddress = options.changeAddress || null;
+  this.round = options.round || false;
+  this.rate = options.rate || null;
+  this.maxFee = options.maxFee || null;
+
+  // Needed for size estimation.
+  this.m = options.m || null;
+  this.n = options.n || null;
+  this.witness = options.witness || false;
+  this.script = options.script || null;
+}
+
+/**
+ * Initialize the selector with coins to select from.
+ * @param {Coin[]} coins
+ */
+
+CoinSelector.prototype.init = function init(coins) {
+  this.coins = coins.slice();
+  this.outputValue = this.tx.getOutputValue();
+  this.index = 0;
+  this.chosen = [];
+  this.change = 0;
+  this.fee = 0;
+  this.tx.inputs.length = 0;
+
+  switch (this.type) {
+    case 'all':
+    case 'random':
+      this.coins.sort(sortRandom);
+      break;
+    case 'age':
+      this.coins.sort(sortAge);
+      break;
+    default:
+      throw new FundingError('Bad selection type: ' + this.type);
+  }
+};
+
+/**
+ * Calculate total value required.
+ * @returns {Amount}
+ */
+
+CoinSelector.prototype.total = function total() {
+  if (this.shouldSubtract)
+    return this.outputValue;
+  return this.outputValue + this.fee;
+};
+
+/**
+ * Test whether the selector has
+ * completely funded the transaction.
+ * @returns {Boolean}
+ */
+
+CoinSelector.prototype.isFull = function isFull() {
+  return this.tx.getInputValue() >= this.total();
+};
+
+/**
+ * Test whether a coin is spendable
+ * with regards to the options.
+ * @param {Coin}
+ * @returns {Boolean}
+ */
+
+CoinSelector.prototype.isSpendable = function isSpendable(coin) {
+  var height = this.height;
+  var maturity = constants.tx.COINBASE_MATURITY;
+  var conf;
+
+  if (!(height >= 0))
+    return true;
+
+  if (this.confirmations > 0) {
+    if (coin.height === -1)
+      return this.confirmations <= 0;
+
+    conf = height - coin.height;
+
+    if (conf < 0)
+      return false;
+
+    conf += 1;
+
+    if (conf < this.confirmations)
+      return false;
+  }
+
+  if (coin.coinbase) {
+    if (height + 1 < coin.height + maturity)
+      return false;
+  }
+
+  return true;
+};
+
+/**
+ * Get the current fee based on a size.
+ * @param {Number} size
+ * @returns {Amount}
+ */
+
+CoinSelector.prototype.getFee = function getFee(size) {
+  var fee;
+
+  if (this.round)
+    fee = bcoin.tx.getRoundFee(size, this.rate);
+  else
+    fee = bcoin.tx.getMinFee(size, this.rate);
+
+  if (fee > constants.tx.MAX_FEE)
+    fee = constants.tx.MAX_FEE;
+
+  return fee;
+};
+
+/**
+ * Fund the transaction with more
+ * coins if the `total` was updated.
+ */
+
+CoinSelector.prototype.fund = function fund() {
+  var coin;
+
+  while (this.index < this.coins.length) {
+    coin = this.coins[this.index++];
+
+    if (!this.isSpendable(coin))
+      continue;
+
+    // Add new inputs until TX will have enough
+    // funds to cover both minimum post cost
+    // and fee.
+    this.tx.addInput(coin);
+    this.chosen.push(coin);
+
+    if (this.type === 'all')
+      continue;
+
+    // Stop once we're full.
+    if (this.isFull())
+      break;
+  }
+};
+
+/**
+ * Initiate selection from `coins`.
+ * @param {Coin[]} coins
+ * @returns {CoinSelector}
+ */
+
+CoinSelector.prototype.select = function select(coins) {
+  this.init(coins);
+
+  if (this.hardFee != null)
+    this.selectHard(this.hardFee);
+  else
+    this.selectEstimate(constants.tx.MIN_FEE);
+
+  if (!this.isFull()) {
+    // Still failing to get enough funds.
+    throw new FundingError(
+      'Not enough funds.',
+      this.tx.getInputValue(),
+      this.total());
+  }
+
+  // How much money is left after filling outputs.
+  this.change = this.tx.getInputValue() - this.total();
+
+  return this;
+};
+
+/**
+ * Initialize selection based on size estimate.
+ * @param {Amount} fee
+ */
+
+CoinSelector.prototype.selectEstimate = function selectEstimate(fee) {
+  var size;
+
+  // Initial fee.
+  this.fee = fee;
+
+  // Transfer `total` funds maximum.
+  this.fund();
+
+  // Add dummy output (for `change`) to
+  // calculate maximum TX size.
+  this.tx.addOutput({
+    // In case we don't have a change address,
+    // use a fake p2pkh output to gauge size.
+    script: this.changeAddress
+      ? Script.fromAddress(this.changeAddress)
+      : Script.fromPubkeyhash(constants.ZERO_HASH160),
+    value: 0
+  });
+
+  if (this.free && this.height >= 0) {
+    size = this.tx.maxSize(this);
+
+    // Note that this will only work
+    // if the mempool's rolling reject
+    // fee is zero (i.e. the mempool is
+    // not full).
+    if (this.tx.isFree(this.height + 1, size)) {
+      this.fee = 0;
+      return;
+    }
+  }
+
+  // Keep recalculating fee and funding
+  // until we reach some sort of equilibrium.
+  do {
+    size = this.tx.maxSize(this);
+
+    this.fee = this.getFee(size);
+
+    if (this.maxFee && this.fee > this.maxFee) {
+      throw new FundingError(
+        'Fee is too high.',
+        this.tx.getInputValue(),
+        this.total());
+    }
+
+    // Failed to get enough funds, add more coins.
+    if (!this.isFull())
+      this.fund();
+  } while (!this.isFull() && this.index < this.coins.length);
+};
+
+/**
+ * Initiate selection based on a hard fee.
+ * @param {Amount} fee
+ */
+
+CoinSelector.prototype.selectHard = function selectHard(fee) {
+  // Initial fee.
+  this.fee = fee;
+
+  if (this.fee > constants.tx.MAX_FEE)
+    this.fee = constants.tx.MAX_FEE;
+
+  // Transfer `total` funds maximum.
+  this.fund();
+};
+
+/*
+ * Helpers
+ */
+
+function sortAge(a, b) {
+  a = a.height === -1 ? 0x7fffffff : a.height;
+  b = b.height === -1 ? 0x7fffffff : b.height;
+  return a - b;
+}
+
+function sortRandom(a, b) {
+  return Math.random() > 0.5 ? 1 : -1;
+}
+
+function sortInputs(a, b) {
+  return utils.cmp(a.prevout.toRaw(), b.prevout.toRaw());
+}
+
+function sortOutputs(a, b) {
+  return utils.cmp(a.toRaw(), b.toRaw());
+}
+
 /*
  * Expose
  */
diff --git a/lib/primitives/tx.js b/lib/primitives/tx.js
index 2dd34634..d91ccc2d 100644
--- a/lib/primitives/tx.js
+++ b/lib/primitives/tx.js
@@ -1580,6 +1580,23 @@ TX.prototype.getMinFee = function getMinFee(size, rate) {
   return TX.getMinFee(size, rate);
 };
 
+/**
+ * Calculate the minimum fee in order for the transaction
+ * to be relayable, but _round to the nearest kilobyte
+ * when taking into account size.
+ * @param {Number?} size - If not present, max size
+ * estimation will be calculated and used.
+ * @param {Rate?} rate - Rate of satoshi per kB.
+ * @returns {Amount} fee
+ */
+
+TX.prototype.getRoundFee = function getRoundFee(size, rate) {
+  if (size == null)
+    size = this.maxSize();
+
+  return TX.getRoundFee(size, rate);
+};
+
 /**
  * Calculate the transaction's rate based on size
  * and fees. Size will be calculated if not present.
@@ -1594,33 +1611,6 @@ TX.prototype.getRate = function getRate(size) {
   return TX.getRate(size, this.getFee());
 };
 
-/**
- * Calculate the minimum fee in order for the transaction
- * to be relayable, but _round to the nearest kilobyte
- * when taking into account size.
- * @param {Number?} size - If not present, max size
- * estimation will be calculated and used.
- * @param {Rate?} rate - Rate of satoshi per kB.
- * @returns {Amount} fee
- */
-
-TX.prototype.getRoundFee = function getRoundFee(size, rate) {
-  var fee;
-
-  if (size == null)
-    size = this.maxSize();
-
-  if (rate == null)
-    rate = constants.tx.MIN_RELAY;
-
-  fee = rate * Math.ceil(size / 1000);
-
-  if (fee === 0 && rate > 0)
-    fee = rate;
-
-  return fee;
-};
-
 /**
  * Calculate current number of transaction confirmations.
  * @param {Number?} height - Current chain height. If not
@@ -1780,6 +1770,29 @@ TX.getMinFee = function getMinFee(size, rate) {
   return fee;
 };
 
+/**
+ * Calculate the minimum fee in order for the transaction
+ * to be relayable, but _round to the nearest kilobyte
+ * when taking into account size.
+ * @param {Number?} size
+ * @param {Rate?} rate - Rate of satoshi per kB.
+ * @returns {Amount} fee
+ */
+
+TX.getRoundFee = function getRoundFee(size, rate) {
+  var fee;
+
+  if (rate == null)
+    rate = constants.tx.MIN_RELAY;
+
+  fee = rate * Math.ceil(size / 1000);
+
+  if (fee === 0 && rate > 0)
+    fee = rate;
+
+  return fee;
+};
+
 /**
  * Calculate a fee rate based on size and fees.
  * @param {Number} size
diff --git a/lib/wallet/account.js b/lib/wallet/account.js
index c8245197..3e3705a1 100644
--- a/lib/wallet/account.js
+++ b/lib/wallet/account.js
@@ -489,7 +489,7 @@ Account.prototype.derivePath = function derivePath(path, master) {
 
   // Custom redeem script.
   if (path.script)
-    script = new bcoin.script(path.script);
+    script = bcoin.script.fromRaw(path.script);
 
   ring = this.deriveAddress(path.change, path.index, master, script);