  An oscillating scalar field as a quintessence model for dark energy is
proposed. The case of a power-law potential is particularly intriguing and is
the focus of the present article. In this model the equation of state w_{OQ} of
dark energy is a constant determined simply by the power n in the potential
through w_{OQ} = (n-2)/(n+2). Accordingly, when 0 < n < 1, the oscillating
quintessence can provide repulsive gravity and drive the cosmic acceleration.
The condition for oscillation and the constraints from observations are
investigated. For this new scenario a specific natural model with much less
fine tuning is presented.
