Oil companies have paid Mexico's oil regulator nearly US$80 million for seismic data ahead of an auction for deepwater fields, suggesting robust interest in the tender despite a lasting slump in the price of crude.

To date, 13 companies including ExxonMobil Corp. (NYSE: XOM), BP Plc (NYSE: BP) and BHP Billiton paid a total of 1.38 billion pesos (US$78 million) for licenses to use deepwater data, according to a document from national oil regulator CNH seen by Reuters.

Company executives say the sum reflects only a fraction of their spending in the past year to acquire geological data ahead of the Dec. 5 auction, which will feature 10 largely unexplored blocks in the Gulf of Mexico.

The deepwater auction is part of the Round One tender, which is the fruit of an energy reform finalized in 2014 that ended a decades-long production monopoly of state-owned oil firm Pemex.

"It's a commitment to invest in Mexico," an oil company executive said about the purchase of deepwater seismic data.

Speaking on condition of anonymity, the executive said his firm spent more than US$30 million last year on the acquisition of additional deepwater seismic data from private suppliers.

Before deciding whether to bid, companies will want to see contract fine print that has yet to be finalized by the Mexican government.

Oil companies already have spent an additional 346 million pesos (US$19.5 million) on bid packages for the deepwater auction, according to the document.

Global oil prices have fallen more than 70% in the past couple of years, prompting deep spending cuts across the industry and speculation that firms might pass on Mexico's potentially lucrative but costly deepwater projects.

(US$1 = 17.7145 Mexican pesos)