High supply growth and weaker demand due to Opec production cuts pushed spot earnings in the tanker market to the lowest levels in four years, ship brokerage Gibson says. 

While demand growth should resume next year, ongoing high supply in the market will continue to exert "downward pressure on rates." Rates may not show substantial growth until 2019.

In its latest long-term market outlook for tankers, Gibson researchers say "a toxic mix of Middle East production cuts, an anticipated decline in operational and 'forced' tanker storage and rapid fleet growth" are pushing spot earnings much lower this year relative to last year.