Excel 2007 : Looking up value in multiple rows and multiple worksheets

[jfbegay]

I see how a value can be looked up in multiple rows from: [URL="http://www.excelforum.com/excel-general/709497-vlookup-multiple-rows-with-the-same-lookup-value.html"]; but I need to do this in multiple worksheets. How do I do the lookup in multiple rows and multiple worksheets? Example, I need to see all the pH values taken during a year, and for about 10 years.