Feb. 20, 2014 12:14 a.m. ET

Air France-KLM announced plans Wednesday to buy a small stake in Gol Linhas Aereas Inteligentes SA, paying a steep premium to cement a broader alliance with Brazil’s second-largest airline by traffic.

The European carrier would inject $100 million into loss-making Gol, taking a nonvoting stake alongside fellow SkyTeam alliance member Delta Air Lines Inc., which bought into the Brazilian carrier two years ago.

A slide in Brazil’s currency and a weakening economy have dented Gol, the country’s largest domestic carrier, forcing it to seek waivers on debt covenants and explore other ways to enhance liquidity, including a possible flotation of its frequent flier program.

Gol said Air France-KLM would pay $52 million for a 1.5% stake with a reference price of $12.23 a share. Analysts said that equates to a premium of almost 170% above the stock’s close Wednesday. The deal would include a capital increase of around 4.2 million shares.

Gol shares closed at 10.93 reals Wednesday.

Air France-KLM also committed to inject the equivalent of $23 million in commercial, training and marketing services, plus another $25 million over two years if Gol reaches undisclosed synergy targets. The airlines hope to close the deal within six months, subject to regulatory approval.

Gol executives said on a call with analysts that the premium was agreed on the basis of synergies generated by its partnership with Delta, as well as limited “exclusivity” for the expanded partnership with Air France-KLM on trans-Atlantic routes.

Delta and Air-France-KLM are longtime members of SkyTeam, coordinating trans-Atlantic flights, but Gol said it had no plans to join any of the three global airline marketing alliances. The U.S. carrier has a 6.1% stake in Gol, and the planned investment by Air France-KLM is a rare example of two carriers investing directly in the same partner.

The proposed Gol deal would strengthen SkyTeam and Air France-KLM on flights between Europe and South America, where they trail the Iberia arm of International Consolidated Airlines Group SA IAG.MC -0.75% . Iberia is a member of the rival Oneworld group, which includes Brazil’s largest airline, Tam, a member of Latam Airlines Group SALAN.SN +0.12% .

Brazil’s domestic airline market expanded just 0.8% last year, according to the International Air Transport Association. That has forced carriers to cut capacity in an effort to stem losses as the real’s slide has inflated costs.

Gol made a net loss of 705 million reals through the first nine months of 2013, narrowing its year-earlier deficit, although analysts don’t expect the airline to return to profitability until 2015.