The first global crude supply pact in 15 years has underlined the growing energy alliance between Saudi Arabia and Russia, as the depth of the two-year oil slump forces co-operation between once unlikely partners.

Brent crude for February delivery LCOc1 was up 12 cents at $54.01 a barrel by 0752 GMT, after rising 1.7 percent on Thursday. The contract hit its highest since July 2015 at $55.33 on Monday. U.S. crude for January delivery CLc1 was up 32 cents at $51.16 a barrel. Both contracts have lost nearly 1 percent so far this week.

North Sea Brent crude was up 25 cents at $53.25 a barrel by 0940 GMT. U.S. light crude was up 20 cents at $49.97 a barrel.

North Sea Brent crude oil LCOc1 was up 10 cents a barrel at $54.03 by 0950 GMT. U.S. light crude CLc1 was up 15 cents at $51.08 a barrel.

EIA forecasts Brent crude oil prices to average $43 per barrel (b) in 2016 and $52/b in 2017. West Texas Intermediate (WTI) crude oil prices are forecast to average about $1/b less than Brent prices in 2017. The values of futures and options contracts indicate significant uncertainty in the price outlook.

The balance between demand and supply in the oil market will shift earlier than previously expected due to OPEC's output cuts, with prices heading towards $60 a barrel next year, Statoil's chief executive said on Tuesday. Brent crude futures LCOc1 hit $55 a barrel on Monday, the highest level since July 2015, after OPEC agreed on Dec. 1 to curb production by 1.2 million barrels per day (bpd) from January.

International Brent crude oil futures LCOc1 were trading at $54.83 per barrel at 1127 GMT, down 11 cents from Monday's close. U.S. West Texas Intermediate crude was at $51.50 a barrel, down 29 cents.

Russia has also benefited this year from oil's price stabilization and a recent deal between major crude producers to curb output has raised expectations of higher prices next year. The central bank has a medium-term oil price forecast of $40 a barrel.

Brent crude oil futures LCOc1, the global benchmark used to trade oil, soared to its highest since July 6, 2015 to $55.20 a barrel. It last traded at $55.08 a barrel, up 62 cents, or 1.1 percent, at 0946 GMT. WTI crude oil CLc1 traded up 54 cents, or 1 percent, at $52.22 a barrel.

Front-month Brent crude futures LCOc1 were down 45 cents, or 0.8 percent by 0951 GMT (4:51 a.m. ET) from their last settlement at $53.49 per barrel. The contract was up more than 13 percent this week, its biggest gain since March 2009. U.S. West Texas Intermediate (WTI) futures CLc1 were at $50.68, down 38 cents.

Shares in US oil companies soared on Wednesday as Opec ministers meeting in Vienna agreed a plan to cut output by 1.2m barrels per day. “The biggest beneficiaries from this Opec move are the US shale players,” said Mike Kelly, head of exploration and production company research at Seaport Global Securities.

Oil prices slipped on Friday as some investors opted to cash out after Brent touched 16-month a high on Thursday, with optimism over this week's OPEC-Russia accord on cutting output giving way to questions on the "sticking point" of implementing the deal.

U.S. crude oil CLc1 added to overnight gains of 9 percent to reach $50.00 a barrel for the first time since October. Brent crude LCOc1, which soared $4 overnight, touched a six-week peak of $52.73 a barrel.

Brent crude, the international oil marker, rose more than $3.00, or 7.2 per cent, to $49.73 in the late morning in London.

The expected fiscal consolidation and the subdued nature of the recovery are putting in place the conditions for the central bank to resume, in due course, monetary policy easing in a manner consistent with the 4 percent inflation target. However, the pace of easing should take into account the presence of external risks and the need to build credibility under the newly introduced inflation targeting regime.