An oscillation mechanism for use with a spinning fishing reel includes an oscillation gear with a guide pin, rotatably supported within the reel. A slider is disposed within the reel and includes a guide slot formed therein that includes an upper portion and a lower portion. The upper portion includes a first curved portion including a concave side disposed toward a forward edge of the slider and a second curved portion including a concave side disposed toward a rearward edge of the slider. The lower portion includes a first curved portion including a concave side disposed toward the rearward edge of the slider and a second curved portion including a concave side disposed toward the forward edge of the slider. Rotation of the oscillation gear causes movement of the slider along a horizontal center axis of the guide slot.