Exports of Nigeria's Forcados grade of crude oil resumed on Sunday, said Shell on Monday.

The resumption is coming roughly a month after loadings of the medium sweet grade were suspended because of a potential leak at the export terminal.

Sources had told Reuters that exports of the grade, which was scheduled to ship 220,000 barrels per day (bpd) in July, were halted on the evening of July 12 after workers saw fumes near a single buoy mooring where oil was being loaded onto a vessel.

A single buoy mooring is essentially a floating loading facility that allows large tankers to moor offshore to discharge cargoes.

Shell confirmed that injections into the terminal had been curtailed after the report, though no force majeure was declared.

The Shell said the cause of the suspension would be determined by a joint investigation between company and community representatives in tandem with government agencies.

The suspension of Forcados loadings contributed to Nigeria becoming the second-biggest contributor to the drop in OPEC crude oil output in July, a Reuters survey showed.