Middle East oil exporters are locked in an increasingly fierce battle for the world’s fastest-growing markets in Asia, as producers worldwide ship more crude east to compensate for shrinking demand from the US and Europe.

The fight for the trillion-dollar Asian oil market has ended decades of comfortable dominance for Middle East producers, who faced so little competition that refiners in Asia complained of being charged a premium of a dollar or so per barrel above what buyers in Europe or the Americas paid.

The picture has changed as rising US shale supply has sapped demand in the world’s largest crude consumer for the imports it previously bought from Latin America and West Africa. In Europe, years of shaky economic performance and increasing fuel efficiency have shrunk Russia’s traditional market.

With nowhere else to expand, producers are pushing for more sales in Asia. The competition will become even stronger if sanctions on Iran are lifted in coming months and the million barrels per day (mbpd) in Iranian exports that have been choked off returns to the market.

Under sanctions, Iran fuelled the competition by offered discounts, easy credit and free shipping to keep oil flowing. If sanctions are lifted, it may have to be even more aggressive to regain market share.

Amid these shifting market pressures, the Organization of the Petroleum Exporting Countries (Opec) meets to consider adjusting its output target of 30 mbpd.

With oil prices well above $100 a barrel, Opec is likely to leave the target unchanged for now, say delegates who will attend the meetings in Vienna.

“These market dynamics – rising Iraqi output, increase in non-Opec production, particularly in North America, and the potential return of Iran over the longer term – are going to put downward pressure on oil futures and Opec producers will face an increasing challenge going forward,” IHS oil consultant Victor Shum said.