diff --git a/src/computation.nim b/src/computation.nim
index 532a4a604..f0e9286e5 100644
--- a/src/computation.nim
+++ b/src/computation.nim
@@ -11,6 +11,8 @@ proc memoryGasCost*(sizeInBytes: Int256): Int256 =
     totalCost = linearCost + quadraticCost
   result = totalCost
 
+const VARIABLE_GAS_COST_OPS* = {Op.Exp}
+
 type
   BaseComputation* = ref object of RootObj
     # The execution computation
@@ -36,8 +38,11 @@ type
     erasesReturnData*:      bool
 
   Opcode* = ref object of RootObj
-    kind*:      Op
-    gasCost*:   Int256
+    case kind*:      Op
+    of VARIABLE_GAS_COST_OPS:
+      gasCostHandler*: proc(computation: var BaseComputation): Int256
+    else:
+      gasCostConstant*: Int256
     runLogic*:  proc(computation: var BaseComputation)
 
 proc newBaseComputation*(vmState: BaseVMState, message: Message): BaseComputation =
diff --git a/src/constants.nim b/src/constants.nim
index c94665ea0..ff83e5823 100644
--- a/src/constants.nim
+++ b/src/constants.nim
@@ -10,6 +10,9 @@ type
 proc int256*(i: int): Int256 =
   i.initBigInt
 
+template i256*(i: int): Int256 =
+  i.int256
+
 # TODO
 # We'll have a fast fixed int256, for now this works
 
@@ -47,6 +50,10 @@ proc `mod`*(a: Int256, b: int): Int256 =
 proc `div`*(a: Int256, b: int): Int256 =
   a div b.int256
 
+proc log256*(a: Int256): Int256 =
+  # TODO
+  2.int256
+
 proc setXLen[T](s: var seq[T]; newlen: Natural) =
   if s.isNil:
     s = newSeq[T](newlen)
diff --git a/src/errors.nim b/src/errors.nim
index f6f7506f2..ae024add3 100644
--- a/src/errors.nim
+++ b/src/errors.nim
@@ -61,6 +61,10 @@ type
     ## Error raised to indicate an attempt was made to read data beyond the
     ## boundaries of the buffer (such as with RETURNDATACOPY)
 
+  TypeError* = object of VMError
+    ## Error when invalid values are found
+
+
 proc makeVMError*(): VMError =
   result.burnsGas = true
   result.erasesReturnData = true
diff --git a/src/logic/arithmetic.nim b/src/logic/arithmetic.nim
index e3ae6d07a..9249b025d 100644
--- a/src/logic/arithmetic.nim
+++ b/src/logic/arithmetic.nim
@@ -76,20 +76,20 @@ proc sdiv*(computation: var BaseComputation) =
   pushRes()
 
 # no curry
-proc exp*(computation: var BaseComputation, gasPerByte: Int256) =
+proc exp*(computation: var BaseComputation) =
   # Exponentiation
   var (base, exponent) = computation.stack.popInt(2)
   
   var bitSize = 0.int256 # TODO exponent.bitLength()
   var byteSize = ceil8(bitSize) div 8
   var res = if base == 0: 0.int256 else: (base ^ exponent.getInt) mod constants.UINT_256_CEILING
-  computation.gasMeter.consumeGas(
-    gasPerByte * byteSize,
-    reason="EXP: exponent bytes"
-  )
+  # computation.gasMeter.consumeGas(
+  #   gasPerByte * byteSize,
+  #   reason="EXP: exponent bytes"
+  # )
   pushRes()
 
-proc signextend(computation: var BaseComputation) =
+proc signextend*(computation: var BaseComputation) =
   # Signed Extend
   var (bits, value) = computation.stack.popInt(2)
 
diff --git a/src/opcode.nim b/src/opcode.nim
index 82f82e1ef..1917bd693 100644
--- a/src/opcode.nim
+++ b/src/opcode.nim
@@ -4,18 +4,30 @@ import
 
 template run*(opcode: Opcode, computation: var BaseComputation) =
   # Hook for performing the actual VM execution
-  computation.gasMeter.consumeGas(opcode.gasCost, reason = $opcode.kind)
+  computation.gasMeter.consumeGas(opcode.gasCost(computation), reason = $opcode.kind)
   opcode.runLogic(computation)
 
 method logger*(opcode: Opcode): Logger =
   logging.getLogger(&"vm.opcode.{opcode.kind}")
 
-proc newOpcode*(kind: Op, gasCost: Int256, logic: proc(computation: var BaseComputation)): Opcode =
-  Opcode(kind: kind, gasCost: gasCost, runLogic: logic)
+method gasCost*(opcode: Opcode, computation: var BaseComputation): Int256 =
+  if opcode.kind in VARIABLE_GAS_COST_OPS:
+    opcode.gasCostHandler(computation)
+  else:
+    opcode.gasCostConstant
 
+template newOpcode*(kind: Op, gasCost: Int256, logic: proc(computation: var BaseComputation)): Opcode =
+  Opcode(kind: kind, gasCostConstant: gasCost, runLogic: logic)
+
+template newOpcode*(kind: Op, gasHandler: proc(computation: var BaseComputation): Int256, logic: proc(computation: var BaseComputation)): Opcode =
+  Opcode(kind: kind, gasCostHandler: gasHandler, runLogic: logic)
 
 method `$`*(opcode: Opcode): string =
-  &"{opcode.kind}(0x{opcode.kind.int.toHex(2)}: {opcode.gasCost})"
+  let gasCost = if opcode.kind in VARIABLE_GAS_COST_OPS:
+    "variable"
+  else:
+    $opcode.gasCostConstant
+  &"{opcode.kind}(0x{opcode.kind.int.toHex(2)}: {gasCost})"
 
 macro initOpcodes*(spec: untyped): untyped =
   var value = ident("value")
@@ -27,8 +39,12 @@ macro initOpcodes*(spec: untyped): untyped =
     let op = child[0]
     let gasCost = child[1][0][0]
     let handler = child[1][0][1]
-    var opcode = quote:
-      `value`[`op`] = newOpcode(`op`, `gasCost`, `handler`)
+    let opcode = if gasCost.repr[0].isLowerAscii():
+      quote:
+        `value`[`op`] = Opcode(kind: `op`, gasCostHandler: `gasCost`, runLogic: `handler`)
+    else:
+      quote:
+        `value`[`op`] = Opcode(kind: `op`, gasCostConstant: `gasCost`, runLogic: `handler`)
     result[1].add(opcode)
   
   result[1].add(value)
diff --git a/src/runner.nim b/src/runner.nim
index 287c43414..f5a84f04a 100644
--- a/src/runner.nim
+++ b/src/runner.nim
@@ -1,14 +1,30 @@
 import
   strformat, strutils, tables, macros,
   constants, bigints, errors, logging, vm_state,
-  vm / [gas_meter, stack, code_stream, memory, message, value], db / chain, computation, opcode, opcode_values, utils / [header, address],
+  vm / [gas_meter, stack, code_stream, memory, message, value, gas_costs], db / chain, computation, opcode, opcode_values, utils / [header, address],
   logic / [arithmetic, comparison]
 
 var opcodes = initOpcodes:
-  Op.Add: GAS_VERY_LOW add
-  Op.Sub: GAS_VERY_LOW sub
-  Op.Mul: GAS_LOW      mul
-  Op.Div: GAS_LOW      divide
+  # arithmetic
+  Op.Add:         GAS_VERY_LOW        add
+  Op.Mul:         GAS_LOW             mul
+  Op.Sub:         GAS_VERY_LOW        sub
+  Op.Div:         GAS_LOW             divide
+  Op.SDiv:        GAS_LOW             sdiv
+  Op.Mod:         GAS_LOW             modulo
+  Op.SMod:        GAS_LOW             smod
+  Op.AddMod:      GAS_MID             addmod
+  Op.MulMod:      GAS_MID             mulmod
+  Op.Exp:         expGasCost          arithmetic.exp
+  Op.SignExtend:  GAS_LOW             signextend
+
+
+  # comparison
+  Op.Lt:          GAS_VERY_LOW        lt
+  Op.Gt:          GAS_VERY_LOW        gt
+  Op.SLt:         GAS_VERY_LOW        slt
+  Op.SGt:         GAS_VERY_LOW        sgt
+  Op.Eq:          GAS_VERY_LOW        eq
 
 var mem = newMemory(pow(1024.int256, 2))
 
@@ -81,8 +97,12 @@ macro runOpcodes*(computation: untyped, program: untyped): untyped =
 
 # useful for testing simple cases
 runOpcodes(c):
-  stack: @[2.vint, 2.vint, 2.vint]
+  stack: @[2.vint, 2.vint, 2.vint, 2.vint, 2.vint, 2.vint, 4.vint]
 
   Op.Add
   Op.Mul
+  Op.Div
+  Op.Sub
+  Op.Mul
+  Op.Mul  
 
diff --git a/src/vm/gas_costs.nim b/src/vm/gas_costs.nim
new file mode 100644
index 000000000..59f57ba21
--- /dev/null
+++ b/src/vm/gas_costs.nim
@@ -0,0 +1,8 @@
+import
+  strformat, bigints,
+  ../constants, ../opcode, ../computation, stack
+
+proc expGasCost*(computation: var BaseComputation): Int256 =
+  let arg = computation.stack.getInt(0)
+  result = if arg == 0: 10.i256 else: (10.i256 + 10.i256 * (1.i256 + arg.log256))
+  
\ No newline at end of file
diff --git a/src/vm/stack.nim b/src/vm/stack.nim
index a6fe763b8..753fc0ca0 100644
--- a/src/vm/stack.nim
+++ b/src/vm/stack.nim
@@ -168,6 +168,22 @@ proc dup*(stack: var Stack; position: int) =
                       &"Insufficient stack items for DUP{position}")
 
 
+proc getInt*(stack: Stack, position: int): Int256 =
+  let element = stack.values[position]
+  case element.kind:
+  of VInt:
+    result = element.i
+  else:
+    raise newException(TypeError, "Expected int")
+
+proc getBinary*(stack: Stack, position: int): cstring =
+  let element = stack.values[position]
+  case element.kind:
+  of VBinary:
+    result = element.b
+  else:
+    raise newException(TypeError, "Expected binary")
+
 proc `$`*(stack: Stack): string =
   let values = stack.values.mapIt(&"  {$it}").join("\n")
   &"Stack:\n{values}"