I find oiling and waxing unnecessary on a work knife. tarnishing is natural and not harmful to the knife's performance. I think of the tarnish as a badge of honour - a sign of the knife's use history and a reminder that you have a "superior" cutting tool. (Stainless fans please don't kill me...

) The oxidation tarnish is also self-limiting to a degree, as the oxidised layer reduces further oxidation at the surface.
Oxidation is only harmful when it is excessive, ie.- rusting and pitting. This occurs generally only when the knife has been left exposed to the elements for a long time. This tends to happen when the knife is NOT in use.
Where oxidation CAN be harmful is when the edge is not maintained or restored and left to rust between use. The edge has the greatest surface area per volume on the knife so will be oxidised the easiest. Make it a habit to clean the edge by either stropping lightly or touching up the edge (and cleaning) after heavy use.
Keeping the knife clean and dry between use is the best way. Light oiling might be useful for prolonged storage, and waxing is great to ward off those dreaded fingerprints from inconsiderate (and sweaty)admirers on show knives or exhibition pieces.
Of course, don't store a knife in its sheath for prolonged periods. A few months is OK, but longer than that, esp in more humid climates, might cause oxidation on the steel and other metallic parts of the handle etc. due to compounds in the sheath material. I find a custom knife lightly oiled, wrapped in a dry clean towel in a drawer with the rest of my knives, a good way to store the knife. Label the sheaths !! Its amazing how easy it is to mix up sheaths when you start to accumulate a few knives...
Hope it helps. Jason.