Oil prices fell to the lowest settlement in more than a week on Monday, pressured by a stronger dollar, as data showed a decline in OPEC’s September compliance with a production-cut agreement and a weekly rise in the number of active U.S. oil rigs for the first time in a month.

November West Texas Intermediate crude dropped $1.09, or 2.1%, to settle at $50.58 a barrel on the New York Mercantile Exchange—the lowest finish since Sept. 21, according to FactSet data. The front-month contract was up about 2% for last week, up 7.7% for September and logged a quarterly rise of 10.5%. Based on the most-active contracts, however, prices were up around 12% from the August WTI settlement of $46.04 at the end of June. December Brent crude the global oil benchmark, fell 67 cents, or 1.2%, to $56.12 a barrel on London’s ICE Futures exchange.

A recent Reuters poll revealed that output among the Organization of the Petroleum Exporting Countries rose by 50,000 barrels a day in September as the cartel’s overall compliance with its supply-cut deal fell to 86%. Several countries such as Saudi Arabia and Angola bore the brunt of the cuts while other countries such as United Arab Emirates, Ecuador and Iraq engaged in a bit of free riding, only complying by 30%, say analysts. “Weak production discipline within OPEC and the cut exemptions for Libya and Nigeria should mean in our view that closely observed OECD stocks will not fall quite as quickly as expected,” said Commerzbank analysts in a recent report.