An increasingly stretched global refining system means fuel-price volatility is set to become more common, according to top oil executives.

A lack of spare crude-processing capacity due to under-investment, and shutdowns happening more frequently with refiners ramping up on better margins and deferring planned work were common themes at the APPEC by S&P Global Insights conference in Singapore this week. That's left fuels like diesel and gasoline vulnerable to sudden swings when there are unplanned outages.