1. Select the Contours layer in the Contents window.
2. Click the Levels tab in the Properties window.
3. Change both the Minimum contour and Maximum contour to the contour level you wish to export. The map should show you only that contour line.
4. Uncheck the boxes next to Fill contours and Show labels (in both the Major Contours and Minor Contours sections). 
5. Verify the line Style for both Major Contours and Minor Contours is Solid.
   
6. Uncheck the boxes next to all four axes in the Contents window, so you only see the contour line on the screen.
7. Click File | Export and export the contour line to your desired file format (for example, a BLN file), OR click Map Tools | Layer Tools | Export Contours to export to a DXF or SHP file.

If a contour level is represented by more than one line in Surfer, follow the steps above to export the contour level, and then follow these steps to remove the unwanted lines:

1. Click Home | New Map | Base | Base.
2. Select the file exported in step 7 above and click Open. The file is loaded as a base map.
   
3. Right click on the Base(vector) layer in the Contents window and click Start Editing.
4. Individually select or mass select the extra polylines or polygons and press the DELETE key on the keyboard to delete them.
5. Right click on the Base(vector) layer in the Contents window and click Stop Editing.
6. Once the map shows just want you want it to, uncheck the boxes next to all four axes in the Contents window, so you only see the contour line on the screen.
7. Click File | Export and export the contour line to your desired file format (for example, a BLN file).

Updated October 15, 2018