LONDON (Reuters) - Oil gained on Wednesday ahead of an expected extension to production curbs by OPEC and its allies, with further support from industry data showing a larger than forecast drop in U.S. crude stockpiles. Brent crude futures were up $1.04, or 1.71%, at $61.86 a barrel by 1320 GMT. U.S. West Texas Intermediate (WTI) crude futures were up 83 cents, or 1.48%, at $56.93. The Organization of the Petroleum Exporting Countries (OPEC) and allies that include Russia - a group..