The company launched the equity subscription process, supported by the Primary Bid platform, to issue new shares priced at 12p each.
It comes alongside a share placing, raising £590,000, and as it also launches an open offer to raise £810,000.
Highlands said it has so far raised £2.74mln.
“The fundraising allows us to commence drilling at East Denver, where success will be transformational for Highlands, marking our first oil and gas production. I look forward to updating our shareholders in the coming months," said Robert Price, Highlands chief executive.
Dave Mutton, Primary Bid chief operating officer, added: “It's exciting for PrimaryBid to assist another main market listed company to fundraise via our network of retail investors, demonstrating that fair access to new share issues is not just relevant for investors in AIM but for the main market too."
Raisa backing is significant
US oil and gas investment fund Raisa II has provided significant backing to Highlands plans, agreeing to provide some US$32.65mln of cash for drilling.
The agreed package is seen as a long term financing partnership, specifically the fund has earmarked the money for up to 24 wells.
"This is a major financing milestone for Highlands,” Robert Price said in a statement.
“In light of East Denver's compelling economic and operational opportunity, Highlands is pleased to move the project forward.”
Raisa is to provide 28.75% of the well costs, in exchange for a 25% interest in the wells.