A back pack sprayer apparatus for spraying liquids. The apparatus includes an integrally molded structure having an upper tank portion and a lower frame portion. A support stand can be connected to the molded structure, the support stand defining a supporting plane when the apparatus is in an upright position on the ground. The molded structure can have a front side defining a compound curve having an upper concave curve configured to receive an operator's back, and a lower convex curve terminating in a lowermost distal end forming a rearward angle of at least about 20 degrees with an axis normal to the supporting plane. The apparatus can include a pump, a hose, and a sprayer. A cover can be attached to the lower frame portion concealing the pump. The apparatus can include peripheral flanges and a lower drip rail which can help prevent liquid from contacting an operator.