(Bloomberg) -- Schlumberger, the world’s biggest oilfield contractor, said it’s working to collect payment of roughly half a billion dollars from its top customer in Mexico.

“At times in recent periods, Schlumberger has experienced delays in payments from its primary customer in Mexico,” the Houston- and Paris-based company said Wednesday in a federal filing. “Schlumberger’s receivables from its primary customer in Mexico are not in dispute and Schlumberger has not historically had any material write-offs due to uncollectible accounts receivable relating to this customer.”

In 2020, Mexico was home to Schlumberger’s biggest source of work awaiting payment, the contractor said in its annual filing a year ago, but “delays” weren’t associated with the accounts receivable in that country until this year’s filing.

The world’s biggest hired hands of the oil patch have been among the most beaten-up sector of the industry as Covid slashed oil demand. The service providers are now boosting free cash flow as their customers benefit from higher crude prices amid a recovery in demand.

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