Oxidation catalyst compositions include a catalytic material having a BET surface area of at least about 10 m.sup.2 /g and consisting essentially of a combination of bulk ceria and a bulk second metal oxide which may be one or more of titania, zirconia, ceria-zirconia, silica, alumina-silica and .alpha.-alumina. The combination may optionally also include activated alumina having a BET surface area of at least about 10 m.sup.2 /g. The ceria, second metal oxide and optional activated alumina may be mixed together or provided as discrete layers. Optionally, one of platinum or palladium metal may be dispersed on the catalytic material provided that the platinum, when used, is used in limited amounts to preclude excessive oxidation of SO.sub.2 to SO.sub.3. The catalyst compositions may be used for oxidation of oxidizeable components in a gas-borne stream, e.g., in a method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote the oxidation of the volatile organic fraction. The optional inclusion of platinum or palladium promotes the oxidation of gas phase components, e.g., hydrocarbons and carbon monoxide.