In the past I've only ever traded OTC options, and never really thought about the following: If you trade a European OTC option you post/receive cash collateral and on this collateral you receive/pay interest. This is in line with no-arbitrage since one needs to borrow money to post collateral and the interest received on the collateral goes to paying the interest on the loan. Now suppose you trade a listed (European) equivalent. As far as I know you post margin (initial + variation) but you don't receive/pay interest on this margin. Am I right regarding the (no) interest on margin? But if so, isn't the listed equivalent different (different price/vol) from the OTC option? To post margin I'll borrow money on which I have to pay interest, but I am not receiving this interest back from the posted margin, which is different than the OTC case. A basic question perhaps, just never really thought about this as never traded listed.