Service records of treated fence posts installed at the Petawawa forest experiment station at Chalk River, Ontarion have been compiled periodically since 1937 to evaluate the effectiveness of various wood preservatives. Untreated control posts of non-durable Eastern Canadian species had an average service life of from 3.0 to 8.3 years. A number of simple application processes as well as pressure treatments have proved to be very effective as indicated in the service life data presented. Posts of 20 species treated full length by the creosote thermal process are in remarkably good condition after 43 years. Those treated (to 36 inch height) were generally sound at the groundline but their tops were degraded after 18 to 25 years. Simple processes such as cold soaking, sap displacement and diffusion methods produced a service life of over 20 years with various wood species and preservative combinations. Some series of posts treated with copper chrome arsenate have attained a service life of 20 years with all of the posts remaining in service to 1980.