"Most people I speak to believe they will get approval, but the conditions are unknown," said Rickey Ward, NZ equity manager at JBWere.
"Given it's taken such a long time ... it's very hard to believe that they only have to divest four or six petrol stations. It feels like they're going to have to give up a lot more than that."
Mighty River Power gained 2.1 per cent to $2.96.
Sky TV advanced 2 per cent to $5.03. Investors have been wary of Sky as it struggles to keep subscribers, with growing competition from services such as Netflix, and faces higher costs to secure content in the increasingly competitive market.
"It's well off its lows, but it is quite surprising - local institutions don't like it, they think the industry is evolving and changing away from it," Ward said. "That share price has firmed quite nicely on good volume.
"I do wonder whether it's Australian investors - they are the dominant purchaser, and the story has been better received by Australian institutions than local institutions."
Australia & New Zealand Banking Group rose 1.7 per cent to $26.75.
Fletcher Building gained 1.6 per cent to $8.18. "It seems like the company has moved from a downgrade cycle to an upgrade cycle," Ward said.
"Not many companies appear to be undervalued but that one seems to screen pretty well. A lot of offshore investors and some domestics are searching for stocks which haven't been rewarded, that have the potential to surprise, that you're not paying a lot for - that ticks the box."
Air New Zealand advanced 0.9 per cent to $2.885. The airline is benefiting from increased demand from tourism and low fuel prices. It fell 4.7 per cent on Monday after ASX-listed rival Qantas Airlines trimmed plans to expand capacity, a signal it saw leaner times ahead.
Steel & Tube Holdings performed the worst, down 1.7 per cent to $2.28, while Xero fell 1.7 per cent to $17.45.
SkyCity shed 1.5 per cent to $5.15. It has regained ground since the surprise resignation of its chief executive Nigel Morrison triggered a selloff.
"Australian analysts more than domestic ones are optimistic - they've been taking a very positive view on Adelaide in particular."
Outside the main index, Pushpay Holdings fell 10 per cent to $2.20. It has not made any announcements, but rallied to an all-time high of $2.75 a week ago and has fallen back since.
"They would have to disclose if it was something of materiality regarding the company's earnings, positive or negative," Ward said. "They've been asked to disclose a number of times, and they've been consistent in their message that they've fulfilled all their obligations."
