Mexico's Health Secretary Jorge Alcocer said Friday that the latest victims who were severely burned died between Wednesday and early Friday. He said hospitals continue to treat about 40 injured victims.
The victims were gathering gasoline from an illegal pipeline tap in the central state of Hidalgo a week ago when the gas ignited, littering an alfalfa field with charred bodies.
About half of those who initially survived have since died of their injuries.
A total of 14,894 illegal taps were found throughout Mexico in 2018. Experts have long said that workers and union officials of the state-owned oil company, Pemex, have been involved in the massive fuel thefts.
The union, run autocratically by old-style union boss Carlos Romero Deschamps, has been marked by corruption scandals for decades.
On Friday, a dissident union movement, calling itself Petromex, announced a legal challenge to unseat Romero Deschamps and form a new union.
About 100 Pemex workers gathered in front of the Labor Department offices in downtown Mexico City to demand the new union be registered, a first step that could lead to a vote between competing unions to see who gets to represent the company's 114,000 workers.
Petromex spokesman Oscar Solorzano said Romero Deschamps "is the country's No. 1 thief; that's how the Mexican public sees him."
Petromex activists said about 120 workers signed the petition for their union to be recognized, but they claimed to have support or expressions of interest from about 25,000 workers.
Activist Wilber Santiago Jimenez said Pemex employees had also been required to pay officials of the current union for the right to work.