C# :: Finding The Size Of Multiple Lists

I am writing a Windows Form program, and currently it has 3 Lists. I need to loop through all three, and use each possible combination, so am using three nested for loops.

I found that if the outer loop had less elements than one of the inner loops/lists, some were missed off, as I need to save all the possible combinations of list a + b + c.

This is what I wrote:

Code:
public int CalculateOrderToProcessLists()//for three lists
{
int order = 0;
if (sListOne.Count() > sListTwo.Count() && sListTwo.Count() > sListThree.Count())
{
order = 123;

[Code ....

My problem is I would like to be able to have 4 (or more if possible) lists, and to calculate what order to process the lists will be exponentially more complex.

Any better way of comparing the sizes of the lists, so that I can use the nested loops of say 4 lists, but being able to use N number of lists would be awesome.