HS125 First Officer reports being confused by the Charlie departure from OERK. A turn to heading 075 degrees is initiated after takeoff from Runway 15L; while the flight should have flown to KIA then proceeded out the KIA 150 degree Radial.

Narrative

ATC clearance is not given in Riyadh until the aircraft starts taxiing but those familiar with the airport can brief on what is expected on the ground. Runway in use was 15L with a departure to the west. The Charlie departure off of 15L has you turn to a heading of 075 degree's and maintain 6;000 FT after takeoff. We had previously done this departure earlier in the week and nothing was said to us and our routing was the same. There is a fine note on the chart that says if first point is SODIB that the departure should be straight ahead to KIA VOR and then proceed outbound on the 150 degree radial. Our first point was OVEKU and then SODIB. We were told to contact ATC after takeoff and as soon as we reached 400 FT AGL I checked in with Riyadh departure. He cleared us direct to SODIB. We had just started our left turn though and could've still gone to the right. He queried direction we were going and said west bound departure's should go to KIA VOR before proceeding to the west. He gave us a heading to fly and then re-cleared us to SODIB. We apologized and nothing further was said to us. If the departure specifically says; 'Charlie Departure to the West;' why would they still include the verbiage and pictorially display the left turn to the east if nobody should be going that way. The chart is very confusing and I have spoken to other pilots who were unaware of going straight out to the VOR if proceeding westbound. We had no conflict with any other traffic and we proceeded without disrupting the airspace. If this chart could be changed; it would prevent this potentially unsafe condition from happening again.