Oil cartel OPEC on Tuesday said speculators and a weak US dollar have contributed $45 a barrel to push the international crude oil prices to a high of $142 a barrel.

The Organization of Petroleum Exporting Countries (OPEC), which accounts for worlds 40 per cent of the oil production, also said its raising the production was not a solution to the high prices.

"Almost 60 per cent of that (price increase in one year) is due to combination of dollar devaluation and speculation," OPEC President Chakib Khelil told reporters on sidelines of the 19th World Petroleum Congress in Madrid.

Crude prices have doubled in the past one year, a phenomenon OPEC member-countries and consuming nations like India have blamed on speculators.

In oil price of over $142 per barrel, nearly $45 is premium, he said. 

Consequences of sub-prime crisis led to a devaluation of dollar that allows speculators to intervene in prices, he said, adding increasing output alone would not bring down prices and speculative activities need to be curbed. 

"Increasing output alone will not bring down prices as we have seen in the case of Saudi Arabia that increased output by 5,00,000 barrels per day in two installments but prices have not come down," he said.

"US senators are investigating into speculation loopholes. It may not be plugged but can be avoided," he added.