Six of 25 oil and natural gas contracts that Mexico awarded last December went unsigned after the winning bidders failed to provide the required financial guarantees and will be assigned to other auction participants.

Juan Carlos Zepeda, president of the National Hydrocarbons Commission, or CNH, Mexico’s oil regulator, said those license contracts for onshore oil blocks would be awarded to the second-place bidders.

“As of (Tuesday), the CNH will begin the process of claiming the bid security bonds, which amount to $390,000 and will be deposited in the Mexican Oil Fund for Stabilization and Development,” Zepeda said of the contracts awarded in December to the companies Geo Estratos, Strata and Sarreal.

Those contracts for onshore petroleum and natural gas blocks were awarded in December as part of Mexico’s historic Round One oil auction, the first to be held after a 2013 overhaul ended state-owned energy company Petroleos Mexicanos’ 75-year-old monopoly and opened Mexico’s hydrocarbons sector to private investment.

The six fields “represent resources with a high degree of certainty and good profitability” because the “average cost per barrel is less than current oil prices on the international market,” Energy Secretary Pedro Joaquin Coldwell said Tuesday.