Lots of different finishes you could use depending on how you want it to look. For practicality, durability and ease of application we typically use hard-wax oils on our staircases, most joinery and even our timber floors. Sarah is right that Danish oil can do the job though we've found that hard-wax oils are that much more durable, require less maintenance and reapplication. They also come in neutral (colourless) or in a range of colours from white through to dark, enabling you to finetune the pigment to your specification. Do you want the pine's natural colour and grain left faint and neutral or would you like it really enriched, enhanced and more golden? Or would you like a different hue altogether? We can recommend you a product or two that would do the job nicely.

OK in that case and bearing in mind the sheen level you want we would recommend the Treatex range of hardwax oils. Either 2-3 coats of Treatex clear satin hardwax oil on its own (the timber will take on a warmer tone without 'orangeing') or - if you prefer the timber to look a little lighter/less warm overall - the above following a base coat of one of the lighter Treatex 'colour tones' such as 'Spruce' or 'Light oak'.

Osmo make some good stuff too so definitely worth a go. We used to use their stuff quite a bit