Major oil field services firms Halliburton (HAL) and Schlumberger (SLB) say they’re not being paid in a timely manner by their top customer in Mexico— believed to be oil giant Pemex— which has faced allegations of corruption for decades. The disclosures came in the company’s most recent annual reports.

In Halliburton’s latest 10-K, the company revealed this customer accounted for approximately 10% of receivables as of December 31, 2021, or approximately $366 million according to our estimate:

“While we have experienced payment delays in Mexico, these amounts are not in dispute and we have not historically had, and we do not expect, any material write-offs due to collectability from this customer.”

No other country or single customer accounted for more than 10% of Halliburton’s receivables at year end 2021.

The situation is worse financially for Schlumberger. In its latest 10-K, the company suggests its having trouble collecting approximately $500 million in Mexican receivables:

“At times in recent periods, Schlumberger has experienced delays in payments from its primary customer in Mexico…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.”