Well, the gold standard is to find fares (expertflyer.com will help you out here) then find inventory that matches the fares.
United has a live $69 base fare K fare from EWR-OSL; find inventory to match and you're good to go. ITA Matrix (matrix.itasoftware.com) will help you do a fairly broad search, like "departure date within 1 month of X day and total journey length Y--Z days."
If you don't have the time for that stuff, follow the folks at theflightdeal.com, who as near as I can tell have software scraping fares on a few hundred key routes and make blog posts when they see particularly low fares; see e.g. http://www.theflightdeal.com/2014/10/31/united-466-newark-os... .
United has a live $69 base fare K fare from EWR-OSL; find inventory to match and you're good to go. ITA Matrix (matrix.itasoftware.com) will help you do a fairly broad search, like "departure date within 1 month of X day and total journey length Y--Z days."
If you don't have the time for that stuff, follow the folks at theflightdeal.com, who as near as I can tell have software scraping fares on a few hundred key routes and make blog posts when they see particularly low fares; see e.g. http://www.theflightdeal.com/2014/10/31/united-466-newark-os... .
The SFO-OSL $512 fare was posted in March; don't think it's still valid, http://www.theflightdeal.com/2014/03/07/united-512-san-franc... .