Oil producers’ cartel Opec has told the BBC that compliance with production targets fell to 50-56% last month compared with 80% a year ago.
Secretary General Abdalla Salem El-Badri told the BBC’s Business Daily programme the move was “worrying”.
“The risk is you see a lot of oil in the market and no one is buying it. Then the price will come down.”
At its last meeting in Angola, Opec decided not to change the amount of oil being produced by its members.
Oil prices have doubled from their lows of December 2008, but are way down on the record $147 a barrel reached in July 2008. US light, sweet crude is trading at about $78 a barrel – its highest level in two weeks.