Xero

Xero is a petroleum company in the Grand Theft Auto series, featured in the HD Universe titles.

Grand Theft Auto IV and Grand Theft Auto: Chinatown Wars
Unlike its competitors, such as RON, Globe Oil, and Terroil, Xero does not appear to have set up any gas stations in Liberty City, although it does operate a refinery at the southwestern corner of the Acter Industrial Park in Alderney. The warehouse in Industrial has the Xero logo painted on storage tanks and on parts of the building, indicating that it was their former refinery before abandoning it and moving to Alderney. Xero storage tanks and faded advertising of the brand can also be found in selected parts of Liberty City, and Xero sponsorship vinyls are visible on certain Bati Customs designs.

Grand Theft Auto V and Grand Theft Auto Online
The company owns several inaccessible filling stations across San Andreas. ATM's and Jerry Cans are usually found at these gas stations. There is also an industrial building on Greenwich Parkway in the Los Santos International Airport, as well as a refinery in Blaine County.

Xero Gas appears to be a primary vehicle racing sponsor, in a similar manner to other companies such as RON and LTD. In the enhanced version of the game, they appear as a primary sponsor on the Rapid GT Classic, Sentinel Classic, Jester Classic, Comet Retro Custom and Lynx. They also have their logo sponsored on the Xero Blimp. While not major sponsors on the livery, they also appear on various other liveries, including the Jester (Racecar) and Massacro (Racecar).

Influence
It could be based on, as both have an "x" in their names and share the same colors in their logos. Its name and logo design also appear to be similar to that of Xoomer in Grand Theft Auto: San Andreas. It might also be based on, given the fact that much like Chevron, it has refineries on the East Coast, yet no presence in gas retailing there. Xero's logo also features "Chevron arrow" shapes in the 'X' letter on their logo in red and blue much like the Chevron logo.

Xero's vintage logo is very likely based on the logo for due to the oval shape with the blue and white colours with red text in the middle. This is very likely a reference to Exxon buying and subsequently the Esso brand in 1972, after which most Esso stations in the U.S. were replaced by Exxon ones.

In GTA Online, the Xero to Hero livery for the Sentinel Classic is based on the Mobil 1 BMW M3 and the Xero livery for the Comet Retro Custom is loosely based on a Mobil 1 1989 Porsche 944, meaning Xero covers the brand in the HD Universe, which is likely a reference to Mobil being merged wit Exxon forming  in 1999 which currently owns the Mobil and Exxon brands.

Grand Theft Auto IV
Xero Gas do not have any filling stations in GTA IV, however there is a Xero Gas refinery within the Acter Industrial Park in Alderney

Grand Theft Auto V and Grand Theft Auto Online
Xero Gas have 5 filling stations across San Andreas:

Trivia

 * The name of the brand is a parody of the term "zero gas", a mockery of the oil crisis.
 * The Xero logo bears strong similarities to that of Xoomer, an oil company featured in Grand Theft Auto: San Andreas.
 * It is possible to destroy the Paleto Bay branch during The Paleto Score.