this is what olly displays
F724B3 mul dword ptr ds:[ebx+esi*4]

and this is the correct disasm
F7 24 B3 mul eax,dword ptr [ebx+esi*4]

what do you mean sir ??
afaik mul is always mul source never heard of two operators on mul

it always multiplies what is on al,ax,or eax by the source and leaves the result in ax,eax, and eax:edx

MUL source

Logic AX . AL * source ; Source is a byte
or
DX:AX . AX * source ; Source is a word
or
EDX:EAX . EAX * source ; Source is a dword (386+)

MUL performs unsigned multiplication.

The carry and overflow flags (CF and OF) are set to 1 if the
high-order of the result (AH,DX, or EDX, respectively) contains
any significant digits; otherwise, CF and OF are reset to 0.


Opcode Format
F6 /4 MUL r/m8
F7 /4 MUL r/m16
F7 /4 MUL r/m32

you are right, this isnt a error

i was just wondering because visual studio disasm displays it as
mul eax, ...

but the use of ax, eax, .. as dest is implicit for mul