Yes escribir is a reflective verb.A reflexive pronoun (pronombre reflexivo ) is used as part of a reflexive verb (verbo reflexivo ) to indicate that someone or something is performing an action on or for itself.
Veo? Vi? Veré?..... present, past or future?
The direct object pronoun would be "la" because la gasolina is feminine. In a sentence you could say
La compro en la estacion de servicio.
Direct object pronouns are placed before the verb generally.