Oil futures fell Monday at the New York Mercantile Exchange as an uptick in the dollar, soft economic data and technical factors conspired to bring down prices.

November light sweet crude lost $1.42 to $80.24 a barrel, and reformulated gasoline dropped 6 cents to $1.98 a gallon. Heating oil slid 4.5 cents to $2.18 a gallon. Natural gas rose 18 cents to $7.05 per million British thermal units.

Earlier, the Institute for Supply Management said its September factory index fell to 52.0 from 52.9 in August, a slightly bigger decline than expected. Because oil is a major economic input, the price of crude oil tends to fall when economic output falters.

According to John Person, president of NationalFutures.com, this could be the beginning of a major technical correction to the downside for oil prices,

"There hasn't been any disastrous news to support existing oil prices, so technical traders are looking for a selloff," Person said. "I think we will see the price of crude fall to somewhere near $76 a barrel by the end of this week."

Meanwhile, energy stocks were mostly higher. Exxon Mobil ( XOM) rose 1.5% to $93.95. Baker Hughes ( BHI) advanced 2.2% to $92.34.

ConocoPhillips ( COP) was downgraded by Deutsche Securities to sell from hold, lowering its shares 0.4% to $87.39.