A field test of untreated and preservative-treated round fence posts has been running at Petawawa, Ont. since 1937. Service life data without preservative treatment on 20 eastern Canadian wood species were developed. In addition, treatments by a variety of pressure and non-pressure processes with waterborne and oilborne preservatives were tested. Thermal immersion in creosote was the most effective non-pressure method used, while brush treatments and cold soaking proved to be ineffective for long-term protection from decay. Pressure treatment using standard waterborne (CCA and ACA) and oilborne (creosote, pentachlorophenol, copper naphthenate and oxine copper) preservatives provided excellent protection. Several preservative/species combinations gave mean service lives well over 50 years.