Global crude oil prices firmed slightly, today, as rising crude output from the United States offset efforts by OPEC and other producers to prop up the market by cutting supplies. Brent crude oil futures rose 17 cents, to 56.41 dollars per barrel. U.S. crude gained 21 cents, to 53.99 dollars a barrel. Investors are focused on shale's response to higher prices, and OPEC compliance. British bank, Barclay's said it expects Brent and US crude prices to average 55 dollars and 53 dollars per barrel, respectively, for the first quarter. OPEC and other producers have agreed to cut output by almost 1.8 million barrels per day for the first half of 2017 to fight a supply overhang that has seen between 1 million and 2 million barrels per day of crude being produced in excess of consumption over the past two years. But U.S. output has risen by around half a million barrels per day since mid-2016, to 8.96 million barrels per day.