Optoacoustic imaging is a highly scalable and versatile method that can be used for optical resolution (OR) microscopy applications at superficial depth yet can be adapted for tomographic imaging with ultrasonic resolution at centimeter penetration scales. However, imaging speed of the commonly employed scanning-based microscopy methods is slow as far as concerned with acquisition of volumetric data. Herein, we propose a new approach using multifocal structured illumination in conjunction with a spherical matrix ultrasonic array detection to achieve fast volumetric optoacoustic imaging in both optical and acoustic resolution modes. In our approach, the laser beam is raster scanned by an acousto-optic deflector running at hundred hertz scanning rate with the beam then split into hundreds of mini-beams by a beamsplitting grating, which are subsequently focused by a condensing lens to generate multifocal structured illumination. Phantom experimental results show that 10 x 10 x 5 cm 3 volumetric imaging can be accomplished with spatial resolution around 29 μm. We believe by further speeding up the data acquisition in the further, the system will be operated in full power, making it possible to study functional, kinetic and metabolic processes across multiple penetration scales.