lookup function formatting

[Ben]

Hi. I am trying to return a value by looking up and intermediate value using
=LOOKUP(A1,Sheet2!$D$2:$B$91,Sheet2!$F$2:$A$91). For example:

Worksheet 1:
A1=well# B1=value from WS2 column F I'm looking for

Worksheet 2:
Column D= data values Column F=well#s A1-A12

Ct Well#
22.23 A1
22.18 A2
22.18 A3
24.36 A4
24.18 A5
24.02 A6
23.2 A7
24.2 A8
24.34 A9
19.15 A10
19.19 A11
19.43 A12

My problem is that when I input A1-A9 into cell A1 I get the proper values.
Inputting A10-A12 always give me the value for A1. Please help.

Thanks,
Ben

[Bearacade]

As per the Excel help file:

The values in lookup_vector must be placed in ascending order