Oil prices declined below $49 on Monday as Goldman Sachs cut its three-month forecast of Brent to $42 a barrel.

Brent and US crude oil are around their lowest since April 2009, following a seventh consecutive week of decline amid a global supply glut.

"Goldman Sachs slashed its 2015 Brent forecast to $50.40 a barrel from $83.75 and US crude to $47.15 a barrel from $73.75."

Reuters reported that the February Brent contract declined to $48.82 a barrel, while US crude oil for February was down $1.12 at $47.24 per barrel.

Gulf producers have shown no signs of reducing output despite an increasing supply glut.

Goldman Sachs slashed its 2015 Brent forecast to $50.40 a barrel from $83.75 and US crude to $47.15 a barrel from $73.75.

In its report, the bank said that despite declining investments in US shale oil, the major driver of the current supply glut, a reduction in production will take longer.

Analysts at the bank were quoted by Reuters as saying: "To keep all capital sidelined and curtail investment in shale until the market has rebalanced, we believe prices need to stay lower for longer."

Venezuelan President Nicolas Maduro met Saudi Arabia’s Crown Prince Salman in Riyadh, Saudi Arabia, to discuss the issue of declining oil prices.

At OPEC’s meeting in November 2014, Saudi Arabia said it would not support prices by reducing production, rejecting calls from other OPEC members.

However, Iran has pledged to help Venezuela curtail declining oil prices.