* Oil prices "stuck in a range" - fuel broker
* China refineries increase throughput
* But crude markets struggle with oversupply (Updates throughout, changes dateline, previous SINGAPORE)
LONDON, July 18 (Reuters) - Oil markets steadied on Tuesday, supported by firm demand but weighed down by high supplies from OPEC and producers in the United States.
Benchmark Brent crude was down 10 cents at $48.32 a barrel by 0720 GMT. U.S. light crude oil was 10 cents lower at $45.92.
"We're stuck in a range that, I think, will be tough to break out of without some kind of political factor coming into play," said Matt Stanley, fuel broker at Freight Investor Services.
In a sign of strong demand, data on Monday showed refineries in China increased crude throughput in June to the second highest on record.
But many markets are well supplied and oil for prompt delivery is trading at heavy discounts to forward futures in several parts of the world. As a result, crude oil prices are trading at only around half the levels seen three years ago.
A deal by the Organization of the Petroleum Exporting Countries with Russia and other non-OPEC producers to cut supplies by around 1.8 million barrels per day (bpd) between January this year and March 2018 has so far failed to tighten the market or push up prices.
Although many OPEC countries have restricted production, others including Nigeria and Libya have been allowed to increase output.
Ecuador, a small producer within OPEC, said on Tuesday it was not cutting its production by 26,000 bpd as agreed due to the country's fiscal deficit, which is expected to hit 7.5 percent of gross domestic product this year.
Oil Minister Carlos Perez said Ecuador was cutting only 60 percent of that figure, putting current output at 545,000 bpd.
"We are not meeting the quota imposed on us because of the obvious needs the country has," Perez said.
A key price indicator will be the release of U.S. fuel storage data by the American Petroleum Institute later on Tuesday, and weekly oil industry figures from the U.S. Energy Information Administration on Wednesday. (Additional reporting by Henning Gloystein in Singapore; Editing by Dale Hudson)