NOVELTY - The method comprises identifying a network comprising customer distribution centers, where each of the customer distribution centers is associated with users of cooking oil, at a first customer distribution center, collecting used cooking oil transported from some of the users associated with the first customer distribution center, introducing the used cooking oil to a first storage unit, providing a mobile reactor configured to convert the used cooking oil into biodiesel fuel under effective reaction conditions, and transporting the mobile reactor to the first customer distribution center.    USE - The method is useful for providing a service to cooking oil users, distributors or other market participants in the production process of biodiesel fuel composition (all claimed), where the biodiesel fuel such as fuel oil or gas turbine fuel is useful in engines and for stationary power applications and for vehicles that travel over land such as trucks, rail such as trains, water such as ships and air such as aircraft.    ADVANTAGE - The method is capable of providing the service to cooking oil users, distributors or other market participants in a cost-effective manner thus energy efficiently producing the biodiesel fuel with reduced amount of wastewater, high yield of qualified glycerin and improved density, viscosity and lubricity and without sulfur content.    DETAILED DESCRIPTION - The method comprises identifying a network comprising customer distribution centers, where each of the customer distribution centers is associated with users of cooking oil, at a first customer distribution center, collecting used cooking oil transported from some of the users associated with the first customer distribution center, introducing the used cooking oil to a first storage unit, providing a mobile reactor configured to convert the used cooking oil into biodiesel fuel under effective reaction conditions, transporting the mobile reactor to the first customer distribution center, feeding some of the used cooking oil contained in the first storage unit to the mobile reactor, feeding an alcohol and a catalyst to the mobile reactor, under the effective reaction conditions and in the presence of the used cooking oil, to produce biodiesel fuel on-site at the first customer distribution center, introducing some of the biodiesel fuel, directly or via a fuel blend, into fleet vehicles associated with the first customer distribution center, at additional customer distribution centers, collecting used cooking oil transported from some of the users associated with each of the additional customer distribution centers, introducing the used cooking oil to individual storage units located at each of the additional customer distribution centers, transporting the reactor to each of the additional customer distribution centers, at each of the additional customer distribution centers, feeding some of the used cooking oil contained in each of the individual storage units to the mobile reactor, and at each of the additional customer distribution centers, feeding methanol and the catalyst to the mobile reactor, under the effective reaction conditions and in the presence of the used cooking oil, to produce biodiesel fuel on-site at each of the additional customer distribution centers, and at each of the additional customer distribution centers, introducing some of the biodiesel fuel, directly or via the fuel blend, into fleet vehicles associated with the additional customer distribution centers. The vehicle is provided to transport fresh cooking oil to each of the users of cooking oil, and is employed to transport the used cooking oil to the first customer distribution center. The network includes 50 customer distribution centers. Some of the biodiesel fuel is utilized to power the vehicle to transport fresh cooking oil to the user of cooking oil and to transport the used cooking oil to the first customer distribution center. A portion of the biodiesel fuel is separately marketed or sold. Each of the mobile reactors is configured to convert used cooking oil into biodiesel fuel under effective reaction conditions. Some of the biodiesel fuel is utilized to power a supplier vehicle to deliver fresh cooking oil to the first customer distribution center, and/or for a return trip for the supplier vehicle back to a supplier location. INDEPENDENT CLAIMS are included for:    (1) a method of converting used cooking oil into biodiesel fuel; and    (2) a system for providing a service to cooking oil users, distributors or other market participants.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a method for providing a service to cooking oil users, distributors or other market participants.