* U.S. crude stocks likely rose by 3.7 mln barrels - Reuters poll
* Coming up: U.S. API oil inventory data at 2030 GMT
* Iran plans 500,000 bpd output increase - Iranian official
* Vitol sees oil struggling to break above $60 by end-2016 (Updates prices, adds comment)
By Koustav Samanta
NEW YORK, Oct 20 (Reuters) - Oil prices eased slightly on Tuesday afternoon reversing earlier marginal gains as market participants waited for direction from two key U.S. oil storage reports.
Brent LCOc1 futures for December delivery fell 35 cents to $48.26 a barrel, a 0.7 percent loss, by 1:56 p.m. EDT (1756 GMT).
U.S. crude CLc1 futures for November, due to expire on Tuesday, fell 66 cents or 1.4 percent to $45.23 per barrel. The December contract Clc2 , which will become the front month on Wednesday, was down 49 cents at $45.79.
The American Petroleum Institute (API) will report stocks data later on Tuesday, and the U.S. Energy Information Administration will release oil inventory data on Wednesday.
"For now, an expected steady expiration of the November WTI contract today and a likely sharp downsizing in Cushing stock build per upcoming API-EIA should keep December values supported above the $46 mark," said Jim Ritterbusch, president of Galena, Illinois-based Ritterbusch & Associates.
Analysts polled by Reuters projected a crude stock build of 3.7 million barrels in the week ended Oct. 16, down from a 7.6 million barrels build in the prior week that was the largest build since April. EIA/S
Alongside the regular focus on U.S. oil inventories, analysts said the market was also keeping a close eye on the meeting of OPEC and non-OPEC oil market experts in Vienna on Wednesday.
The meeting, however, was unlikely to increase the prospect of joint co-operation on supply curbs, OPEC delegates and analysts said. urn:newsml:reuters.com:*:nL8N12J3D3
Major oil exporters in the Middle East are pumping around 2 million bpd more crude oil than needed at the moment, analysts say, filling inventories around the world.
Vitol, the world's largest oil trader, said it believes the crude price will struggle to trade above $60 a barrel next year, as the effects of slowing global demand growth could be compounded by a return of Iranian and maybe even Libyan barrels. urn:newsml:reuters.com:*:nL8N12K2HG
Iran is expected to boost oil production when international sanctions are lifted after it implements the conditions of a nuclear deal agreed with major world powers. Libya is producing around 400,000 bpd. urn:newsml:reuters.com:*:nL8N12J2EJ ID:nL8N12J1PV
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