HOUSTON  A combination of frigid weather, expectations of an improving economy and new tensions between Russia and Belarus catapulted crude oil prices above $81 a barrel on Monday to the highest close in nearly 15 months.

Energy markets are beginning the year with a number of economic signs that could help push prices higher still. Traders viewed reports of increased manufacturing activity and passenger car sales in December as indications that the economy was on the mend. Meanwhile, India reported a substantial increase in oil imports.

The eighth consecutive trading session of rising prices was also attributed to nervousness over reports that Russia might charge higher prices and raise export taxes on oil sent to Belarus for refining for European markets. And heating oil futures rose to the highest level in more than a year as cold weather was reported across much of Europe, China and the United States.

Gasoline prices, which had been falling until recently, have reversed course to jump 6 cents in the last week. And with American stockpiles of crude oil sliding by 19.5 million barrels in the last month, higher prices at the pump could be coming in the weeks ahead.