I currently have a CSV that I have built using StringBuilder in C#. 

This CSV is generated by:

Querying the Database using LINQ  

Dumping the Resulting entries into a List  

Looping through the List and pulling out the needed Entities for the CSV  

Formatting and adding the lines to the StringBuilder Variable  

Using StreamWriter Method to export the CSV 

Recently I have been informed that I need this file to be a XLS file instead of a CSV file. I have done some research, but I am a beginner coder, and am unsure of how to convert this file to an XLS or create an XLS from my Queried Data. Keeping in mind that after I retrieve the results of my query,the Data must be formatted properly before the export.

Ex.  

Database Product Number: 9999-0000  

Adjacent Systems Product #: 99990000BA

Database Date: 12/05/2010  

Adjacent Systems Date: 2010/05/12 

What is the best way I can go about creating an XLS or converting to an XLS from my current Code/Data?