SINGAPORE  - Abu Dhabi National Oil Company (ADNOC) has informed some term buyers that it will reduce the contractual volume of crude loading in January, three sources familiar with the matter told Reuters on Tuesday.

The supply of its flagship Murban crude grade will be reduced by 20%, while the volume of two other grades - Upper Zakum and Das - will be cut by 15%, the sources said.

ADNOC will also trim the supply of Umm Lulu crude grade by 5% in January, one of the sources said.

ADNOC declined to comment.

The January term crude oil supply cut was smaller compared with a roughly 20% overall reduction by ADNOC in December. 

OPEC+, a group which includes the United Arab Emirates, agreed last week to slightly ease their deep oil output cuts from January by 500,000 barrels per day (bpd).

The group also agreed to hold monthly meetings starting in January to decide on further production adjustments that will add no more than 500,000 bpd a month.  

(Reporting By Shu Zhang; Additional reporting by Maha El Dahan in Dubai; Editing by Tom Hogue and Edmund Blair) ((shu.zhang@thomsonreuters.com; +65-6870-3549; Reuters Messaging: Twitter @shuzhang4))