GENEVA – Women working in oil trading at Glencore earn 28% less pay on average than men and receive bonuses that were 57% lower.

The income disparity, disclosed by the second-biggest independent oil trader under UK government-mandated pay gap reporting, underscores the lack of women in senior roles at the largest commodities trading houses.

The vast majority of the 348 employees at Glencore’s London offices work in the firm’s oil trading operations, including the traders themselves and their support staff. While women account for about a third of that number, they comprise only 16% of the top quartile for pay, the figures show.

A study of the executive committee members of the top 40 commodity trading houses this week by Bloomberg News revealed that women account for just 4.2% of the senior executive roles, a level well below US financial institutions and UK blue-chip companies.

The higher level of males seeking careers in commodities trading “has led to a greater number of men than women in senior and other positions that attract a higher level of pay,” Glencore said in a report accompanying its UK disclosure.

The Baar, Switzerland-based commodities trading and mining firm said it is “committed to supporting women going on and returning from maternity leave” and “taking an equal approach to family-friendly practices, including flexible working.”

Glencore’s oil trading business is centered in London while its metals and coal trading operations are based in Switzerland. While 40% of its trading employees are women, none of its executive committee members, who lead the firm’s day to day operations, are female.

Glencore’s 57% gender gap in oil trading bonus, compares with a 62% gap at the trading unit of Royal Dutch Shell. That compares with a 28% gap for the rest of Shell’s British operations.

Overall bonus pay for women working at BP was 64% less than men. The company does not break out separate data for the trading unit.