A containment reservoir for a liquid, such as petroleum oil, comprising, a walled ground containment space or pit, opening upwardly, with the space containing a liquid impervious flexible liner generally following the contour of the space, and with the liner comprising a layer of pervious fabric material having on at least one of its sides a layer of liquid impervious material, such as rubber, the liner being operable to prevent escape of liquid through the liner from the containment space; means are provided coacting with the liner covered containment space for removing liquid from the reservoir. A covering layer of pervious fabric material filters anything, including liquid, passing into the reservoir. A method of forming the reservoir from predetermined width strips of liner stock, and a method of retaining and salvaging oil spilled along a railroad track environment is also disclosed.