I was recebtly asked this question from a colleague and it was a difficult question to answer as they are both very similar.
The main differences lie in the rights and obligations of the buyer and seller. With an option, the buyer and seller have the right to buy an asset at any time during the life of the contract whereas with futures both the buyer and seller have agreed to buy, and sell, an asset at a future and are obliged to fulfill their agreement.
Another main difference are the premiums paid when dealing.
An option is more flexible than a future and can be a safeguard against any loss of an asset which is why dealers charge a premium for options to be put in place.
A future has to be sold at the agreed time whether it has made a loss or not and therefore does not have a premium associated with it.
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