Ann: Trading Halt, page-32

read the ASX Guidance Note 16 , it is all about trading halts
basically here are the quick points

- dual listed companies should apply on other exchanges but it is not compulsory and will depend on the other exchanges disclosure regulations

- ASX doesn't like trading halts and will only grant if (clause 2.1)
1. trading in the security can occur and the whole market is not reasonably informed
2. there could be false or disorderly market in the security
3. it is required to manage the continued disclosure obligations

further (clause 2.2)

- ASX will only grant If it is satisfied on circumstances to justify interrupting trading. the applying entity has to provide information why it cannot make an immediate announcement and the events it expects to happen so it can make the announcement


so in this case

no oil and a duster at first section would not justify a TH
oil shows and need 24-48hrs for analysis and confirmation would justify TH