The changing global oil refining picture has seen several mid-range to large companies spin off their downstream operations in recent years, but the trend has yet to travel up the food chain to the world’s largest oil companies, despite pressure from investors to do so.

Examples of companies that divested downstream assets include Hess and Marathon, with ConocoPhillips being the largest to shun the vertical integration model by splitting their refining unit into separate company Phillips 66 in 2011.

“Investors say: ‘We don’t need you to be an integrated company’ …They say: ‘We can buy BP for upstream and Valero for downstream. And we will create our own oil company’,” said Marcel Van Poecke, who runs a fund at private equity giant Carlyle, as reported by Reuters.

According to other experts quoted in the article, the majors still value their downstream businesses enough to hold on to them because refining is expected to produce double-digit percentage returns on average capital employed – a key oil company performance metric – in coming years.

Maintaining operations in developing economies can also add value as global oil product consumption shifts from west to east and from developed to emerging markets. Developing world governments also often like to partner with companies that have refining operations, as this can facilitate market access for the crude oil produced upstream.

On an interesting side note, we’re not sure why Reuters considers Italian oil company Eni a “major oil company,” a determination usually reserved for the world’s largest privately-held integrated companies. The roughly 30% state-owned firm was ranked number 21 in the 2013 Energy Intelligence Top 100: Ranking the World’s Oil Companies, which is based on oil & gas reserves and production, product sales and refining capacity.