Yes, P waves are longitudinal. P waves, also known as primary waves, are the fastest moving seismic waves and they cause particles of the medium through which they travel to oscillate back and forth in the same direction as the wave's movement. This is in contrast to S waves, or secondary waves, which are transverse and cause particles to move perpendicular to the direction of the wave's travel. read more >>

For seismic waves through the bulk material the longitudinal or compressional waves are called P waves (for "primary" waves) whereas the transverse waves are callled S waves ("secondary" waves). Since any material, solid or liquid (fluid) is subject to compression, the P waves can travel through any kind of material.read more >>