Heat the oil in a skillet. Add the salmon and dry for 1 minutes each side. Reduce the heat and cook for a further 3-5 minutes on each side or until a fork will slide in easily next to the bone. Transfer the salmon to a dish, cover and keep warm.
Melt the butter in the skillet. Add the vinegar and capers and bring to a boil, then simmer for 2 minutes, stirring occasionally. Remove from the heat, season to taste and stir in the parsley. Pour the sauce over the salmon steaks.