Oil prices slipped for a fourth day on Wednesday on forecasts of higher refinery production in the United States that would ease worries over fuel supplies during peak summer demand.

London Brent crude, currently seen as more representative of the world market, eased 39 cents to $74.69 a barrel by 1055 GMT, after tumbling $1.78 on Tuesday. U.S. crude for September traded 25 cents lower to $73.31.

U.S. gasoline stocks were seeing rising 400,000 barrels last week as refinery usage increased sharply, although strong summer demand is likely to have limited the potential for a larger build, a Reuters survey of analysts showed .

The recent return of some U.S. refineries from unplanned outages is a bearish element, said Harry Tchilinguirian, oil analyst at BNP Paribas.

While U.S. gasoline imports in this week's data are likely to stay subdued, higher refinery runs and more blending should lift domestic supply.

U.S. crude stocks were seen falling 1.2 million barrels last week in the government data due later on Wednesday, dropping for the third week running, but this would still leave stocks about 5 percent above the level this time last year.

There were also expectations that crude supplies from OPEC were rising.

Oil consultant Petrologistics, which tracks tanker shipments, said overall OPEC output was set to rise 300,000 barrels per day to 30.7 million bpd this month, as producers took advantage of near record crude oil prices.

The Brent market's losses from an 11-month high above $78 last week have stopped a near two-month rally that was sustained by speculative buying and worries over summer gasoline supplies, but OPEC has so far resisted raising its output ceiling.

OPEC's second-biggest producer Iran said on Tuesday the exporter group, which agreed to cut output last year as prices were sliding, would ramp up output if necessary.

This follows similar remarks from OPEC President Mohammed al-Hamli who said on Sunday the organization was worried high oil prices might hurt the world economy.

Production from non-OPEC Russia will remain steady until 2020, its Economy Ministry said on Tuesday, broadly confirming the outlook by the International Energy Agency.

The ministry said in its long-term economic outlook that it expected production from Russia, the world's second-largest oil exporter after Saudi Arabia, to level off at 10.6 million barrels per day between 2015 and 2020.

(Additional reporting by Neil Chatterjee in Singapore)