You can have a maximum of 10 Fuel, each race normally costs 1 fuel

Boss races cost the following fuel amounts:

Boss 1 - 7 > 1 Fuel

Tier C
Boss 1 - 5 > 1 Fuel
Boss 6 - 7 > 2 Fuel

Tier B
Boss 1 - 2 > 1 Fuel
Boss 3 - 5 > 2 Fuel
Boss 6 - 7 > 3 Fuel

Tier A
Boss 1 - 2 > 2 Fuel
Boss 3 - 4 > 3 Fuel
Boss 5 - 6 > 4 Fuel
Boss 7 > 6 Fuel

Tier S
Boss 1 > 2 Fuel
Boss 2 - 3 > 3 Fuel
Boss 4 - 5 > 4 Fuel
Boss 6 > 6 Fuel
Boss 7 > 8 Fuel

Fuel recharges 1 every 12 minutes, to get more, tap the Fuel icon on the top bar, where you can:

- Watch an ad for 1 fuel

- Complete refill for 100 Gold

- Purchase a Permanent upgrade which increases your maximum Fuel capacity by 2. You start with 8 Fuel, and you can have a maximum of 10. Buying the permanent upgrade also refills your entire capacity to max once.