The rise in oil supplies on global markets does not justify the sharp drop in crude prices, a top OPEC official said Sunday, arguing speculation might be a contributor.

“We want to know the main reasons that have led to such a drop in oil prices,” said Abdalla Salem el-Badri, secretary general of the Organization of the Petroleum Exporting Countries.

“When we look at supply and demand, there is a rise (in supply) but only a modest one that should not have led to this 50-percent drop,” he told reporters at a conference in Dubai, adding that a continued drop could mean that “speculation is strongly contributing to pushing prices down.”