What should I include as the cost or other basis?

For positions closed out or sold, enter the cost or other basis, plus commissions paid. Include nondeductible interest and carrying charges that are allocable to part of the straddle. If any part of an unallowed loss from an offsetting position established in an identified straddle after October 21, 2004 increased your basis in the position, also include that amount.

See Publication 550  for more details.