Market power gives firms the ability to engage in unilateral anti-competitive behavior. Some of the behaviours that firms with market power are accused of engaging in include predatory pricing, product tying, and creation of overcapacity or other barriers to entry. Unilateral market power is one of the most common causes of prices being higher than the competitive equilibrium. Market power has been seen to exert more upward pressure on prices than do variations in the quantity of sellers present in the market. This is due to effects relating to Nash equilibria and profitable deviations that can be made by raising prices.