You could make shared lists out of them, then upload them to a new segment as lists. Then you can select 2 at a time and use the TRIM option. Also, you could use intersect to see how many overlap first.
Or. you could export it all using the same view (thus the export will have the same no of columns), add each list in a separate excel sheet and de-duplicate there. Look it up, how to remove duplicates from multiple excel sheets, but you need to be familiar with this kind of operations.
It sounds like a simple Segment Merge function is what you require, as it'll de-duplicate, rather than remove ALL overlapping contacts entirely (which is what Trim would achieve). There's a great guide on Segment combining operations here: Merge, Intersect, Trim
With 4 separate Segments, you'll want to convert them into Shared Lists first as Teiu Codrin rightly points out. However, if you want to maintain any dynamic logic you have in those Segments, make sure to share the Filters as Shared Filters rather than Shared Lists.
I hope that helps. Please keep us posted with how it went
Thanks for sharing the helpful tips. I had been doing Vlopkup in excel and wanted to know if I can do something directly in Eloqua. Looks like I have a few options so I will work on this to see what works best.