The speculator group raised its net long futures and options position in New York by 13,453 to 182,285 in the week to Tuesday, an increase of almost 8 percent.
NYMEX front-month crude prices rose from $97.43 a barrel to $97.50 over the same time period. On Friday, US crude oil prices settled at the highest level in six weeks.
Money manager net long positions were almost unchanged in the ICE Exchange's look-alike US crude contract in London, dropping by 43 to 18,212, a decrease of 0.2 percent.
It is the first time speculators have increased their bets on higher prices for three weeks in a row since the period in late February and early March when the crisis in Libya first threatened to cut oil supplies from the country.
Speculators' combined net longs in New York and London would eventually peak in late April at a record of almost 350,000 contracts before falling by more than 50 percent over the following nine weeks to a low around 160,000 at the end of June. Over the last three weeks net longs have increased again by around 40,000 contracts on a combination of fresh bets on another surge in prices and a reduction in short positions.
US crude oil traded back to near $100 a barrel this week after falling below $90 in early June.
Speculators also increased their net longs in oil products. Money managers raised their net longs in RBOB gasoline futures and options by 4,191 contracts to 61,994, an increase of 7 percent. RBOB gasoline futures rose to $3.1149 a gallon from $3.0982 in the week to Tuesday that the data covers. Money managers also increased their net longs in heating oil, raising them by 3,770 contracts to 44,430, an increase of 9 percent. Heating oil prices rose to $3.0980 a gallon from $3.0876.
