United Airlines has more than doubled its stake in Brazilian carrier Azul.
United has upped its stake from 3.7% to 8% in a private transaction with fellow investor Hainan Airlines.
The deal is worth an estimated $138.3 million.
Hainan still retains a 17.2% stake in Azul.
United is interested in formalizing a joint venture alliance with Azul to capture more of the US-Brazil market.
"Following our initial investment in 2015, connecting traffic between our airlines is at an all-time high, significantly benefiting our customers traveling between the US and Brazil," said United CFO Andrew Levy.
"We continue to look for new ways to provide more connectivity for our customers, and we are excited about today’s announcement as Azul has been a great partner."
United and Azul operate codeshare services via Fort Lauderdale, Orlando and Sao Paulo Guarulhos airports.
Azul chief executive John Rodgerson said the increased stake sets up conditions for deeper cooperation between the carriers especially as Brazil just formally approved an Open Skies deal with the US.
That is expected to usher in a big increase in direct air links.
