Oil prices dropped Monday with the European benchmark contract slipping below $100 a barrel on concerns about fragile demand, heavy supply and a strengthening US dollar.

US benchmark West Texas Intermediate for October delivery fell 63 cents to $92.66 a barrel on the New York Mercantile Exchange, its lowest level since January.

European benchmark Brent oil for October delivery declined 62 cents to $100.20 a barrel, after earlier falling below $100 a barrel for the first time since June 2013.

Matt Smith, analyst at Schneider Electric, cited weak economic data from China and Japan, two major oil consumers, as "not the best start to the week on the economic data front."

China showed a surprising drop of 2.4 percent in imports, while Japan said its economy shrank 1.8 percent on-quarter in April-June, worse than the previously estimated contraction of 1.7 percent.

Analysts also cited reports that suggest lofty supplies of oil remain on the market as refineries in North America and North America shift into maintenance mode and run less crude through their plants.

Tim Evans, analyst at Citi Futures, pointed to "ongoing concern regarding an apparent physical surplus, with some estimating inventories held on tankers used as floating storage at the highest level since 2009."

Finally, the big jump in the dollar against some other leading currencies has also pressured oil.

Because crude is traded in dollars, the commodity becomes more costly outside the US when the dollar strengthens.