Oil prices fell below $61 in international markets today.
On the London market, the price of a barrel after noon was 72 cents lower than at the close of trading at the end of last week, at $60.57.
In the US market, a barrel traded 66 cents lower, at $56.88.
Market sentiment has been dampened by estimates of a supply glut at the end of this year and early next year.
Supply is growing while demand is weak, the International Energy Agency (IEA) reported last week.
Under such conditions, global reserves reached their highest level in four years in August, at 7.9 million barrels, the agency calculated, and the supply surplus should increase significantly by next year at the latest.
Investors are also worried about the US government shutdown due to a disagreement over budget spending.