If Costello allows the CNOOC to take a majority shareholding in...

If Costello allows the CNOOC to take a majority shareholding in WPL, there are a variety of possibilities for HDR.

CNOOC may choose to bail out of the holding altogether, either by finding a single buyer or dumping the stock in the market.
Finding a single buyer would leave HDR in a similar situation to the current position. Dumping the stock would be a short-term disaster.

CNOOC may decide to hold the stock, which would be a positive, as the market would build in a takeover premium, as CNOOC would be perceived as being more aggressive than WPL.

And, of course, CNOOC may decide that HDR represents a tasty morsel alongside WPL and swallow us as well.
Cash offer - complete disaster for long term holders in my opinion as I've stated previously.

If CNOOC had a go for WPL the other oilers would knee-jerk up a bit as the market looks for the next target.

The publicity for our oil market would be good too, attracting predators and fundies who haven't had a look yet.

T