Royal Dutch Shell expects its fourth quarter profits to drop by at least 40 percent to between $1.6 billion and $1.9 billion after a sharp drop in crude oil prices.

The Anglo-Dutch energy giant says it released the figures for shareholders ahead of a vote next week on its proposed combination with BG Group plc. The figures reported were on a current cost of supply basis, the oil industry accounting standard that takes into account fluctuations in the price of oil.

Royal Dutch Shell CEO Ben van Beurden says he's pleased with Shell's performance, and "the momentum in the company to reduce costs and to improve competitiveness."

Energy companies are struggling to adjust to an age of lower prices, with Brent crude hitting 12 year lows in recent weeks.