OPEC oil output is set to fall by 900,000 barrels per day (bpd) this month, a company that tracks OPEC supply said on Friday, pointing to a strong start by the exporter group in implementing a supply cut deal. The Organization of the Petroleum Exporting Countries is cutting its output by 1.2 million bpd from Jan. 1 — its first such deal since 2008 — to prop up oil prices. “OPEC supply is on track to decrease by 900,000 bpd in January, suggesting a high level of compliance thus far into the production curtailment agreement,” Daniel Gerber, chief executive of Petro-Logistics, said in an email. Petro-Logistics (www.petro-logistics.com) is among a number of consultants that estimate OPEC supply. OPEC itself has yet to publish a figure for its January output. (Reporting by Alex Lawler; Editing by David Goodman)