Sealing composition for plugging and abandoning a wellbore and methods of plugging and abandoning a wellbore are disclosed. Embodiments of a method for plugging and abandoning a wellbore may include introducing a sealing composition into a wellbore and curing the sealing composition to form a plug. The sealing composition may include from 1 weight percent to 20 weight percent of a curing agent, based on the total weight of the composition, and from 20 weight percent to 97 weight percent of an epoxy resin system, based on the total weight of the composition. The epoxy resin system may include an epoxy resin having the formula (OC2H3)—CH2—O—R1—O—CH2—(C2H3O), where R1 is a linear or branched hydrocarbyl having from 4 to 24 carbon atoms; and a reactive diluent having the formula R—O—CH2—(C2H3O), where R is a hydrocarbyl having from 12 to 14 carbon atoms.