UPDATE 6-Oil prices steady as market awaits extended output cut

* OPEC, other producers in Vienna to discuss oil output policy

* Oil exporters look set to extend production cuts by nine months

* High inventories and rising U.S. output undermining OPEC limits (Updates detail, prices, comment; paragraphs 1-2, 5-6)

LONDON, May 24 (Reuters) - Oil prices steadied on Wednesday as investors waited for news from Vienna where ministers from OPEC and other exporting countries were discussing whether to extend production cuts into the first quarter of next year.

Benchmark Brent crude oil was up 10 cents a barrel at $54.25 by 1210 GMT. U.S. light crude oil was unchanged at $51.47.

Both crude benchmarks have gained more than 10 percent from their May lows below $50 a barrel, rebounding on a consensus that the Organization of the Petroleum Exporting Countries and other producers will maintain strict limits on oil production in an attempt to drain a global oversupply.

OPEC has promised to cut supplies by 1.8 million barrels per day (bpd) until June and is expected on Thursday to decide to prolong that cut by up to nine months.

"It could be three, six or nine months," the Iranian Students' News Agency quoted Iran's oil minister, Bijan Zanganeh, as saying.

Most investors expect an extension of nine months.

Sushant Gupta, research director at Wood Mackenzie, told Reuters Global Markets Forum that output cuts were likely to be extended until the first quarter of 2018, and that adherence by OPEC members to the output cuts would probably remain high.

Harry Tchilinguirian, strategist at BNP Paribas, agreed:

"With oil stocks nowhere near OPECs self-assigned objective of the recent five-year average level, an extension of cuts seems all but a forgone conclusion," he said.

BMI Research said the OPEC-led cuts would only result in a balanced market this year, but that from 2018 onward markets would return to oversupply, albeit at a lower level than 2013-2016.

"Over a five-plus-year horizon, oil price growth is in a structural slowdown, pressured by persistent supply gains," BMI Research said.

One reason why markets have not tightened more has been U.S. oil production, which has soared by 10 percent since mid-2016 to 9.3 million bpd. <C-OUT-T-EIA>

Benefiting from a market known as contango, in which future oil prices are higher than those for immediate delivery, U.S. drillers have sold future production in order to finance expanding output.

To stop this, analysts at Goldman Sachs have suggested the oil futures price curve should be pushed into backwardation, where forward prices are below current ones.

But while backwardation might be able to reduce inventories, it is less clear how OPEC could alter the forward price curve, or if that would stop production rising.

(Additional reporting by Henning Gloystein in Singapore; editing by Susan Thomas and Jason Neely)