US crude and Brent futures dropped to fresh 5-1/2-year lows Monday as worries about a surplus of global supplies amid weak demand continued to drag on oil markets.

At 4.30pm GMT (11.30 am ET), West Texas Intermediate crude dropped below $50 a barrel, a decline of more than 4.5% from Friday's close to the lowest level since April 2009.

Brent crude, the international benchmark, was also down more than 5% to below $53 a barrel, the lowest price since May 2009.

Here's the chart of WTI at about 4.35pm GMT (11.35am ET), after it rapidly surged back above $50: