What are the fields in Petrel's IESX seismic horizon file?
X-coordinate
Y-coordinate    
Segment number    
Symbol code 
Two-way time (ms)  
Shot-point number 
CDP number 
Trace number
Line type (2=2D, I=inline, X=crossline) 
2D line name or 3D survey name


The format allows for a column between 8 and 9, for amplitude value — not present in this example.

This is a formatted layout to specific columns. So there is the potential for fields to butt against each other with no spaces between. 

The top 2 lines define the horizon name (after PROFILE) and various picking parameters you shouldn't need. 

This answer comes from Tom Cox (geoscientist at Schlumberger).