During light duty well service operations or logging operations, tools can be lowered into the well on various types of flexible line. Lowering tools on a flexible line is faster and less costly than lowering tools on a drill or tubing string of rigid jointed tubes, which is the alternative.

There have broadly been two types of flexible line, slickline and electric line. Slickline is a single strand of steel wire, and is used to lower mechanical tools and data logging tools (commonly known in the industry as memory tools). Electric line has a flexible multi-stranded load-bearing outer armour surrounding one or more insulated electrical conductors. Electric line is used for conveying electric line logging tools that receive electric power from the surface, and return data to the surface, over the electrical conductors.

As a cable, slickline has the great advantage of lower cost, fast running speeds, and permits a pressure seal to be formed around the line at the wellhead in a device called a stuffing box. This enables safer wireline operations in a live well compared with stranded electric line which is much more difficult to seal effectively. On the other hand, the great benefit of electric line is that it is possible to return real time data to surface over the electrical conductors. This enables the well service operation or logging operation to be more effectively and efficiently managed.