A pin-pin electrode geometry was used to study the velocities of streamers propagating over a flat dielec. surface and in gas close to the dielec. The expts. were done in an argon atm., at pressures from 0.1 to 1 bar, with repetitive voltage pulses. The dielec. surface played a noticeable role in discharge ignition and propagation. The av. speed of the discharge decreased with higher pressure and lower voltage pulse rise rate. It was higher when the conductive channel between the electrodes was formed over the dielec., rather than through the gas. Space resolved measurements revealed an increase in velocity of the discharge as it travelled towards the grounded electrode.