The bank upped Tullow to 'buy' from 'hold' and lifted the price target to 70p from 50p.
"Alongside increased commodity price deck we also allow for improved production expectations from Tullow's Jubilee field," it said. Jefferies highlighted the "material leverage" that Tullow exhibits to higher oil prices.
"In our $70/b oil price scenario, Tullow's Total net asset value increases 61% to 93p and 2022 - 2025 free cash flow yield increases to 33%.
"With the renewed focus on Ghana production and this commodity price sensitivity we upgrade to buy with a 70p price target with the catalyst being evidence of production improvement into 2022."
Jefferies also boosted its stance on EnQuest to 'buy' from 'hold' and upped the price target to 30p from 24p.
"EnQuest is working through some operational challenges at its UK Magnus facility but with completion of the Golden Eagle asset acquisition ahead and significant leverage to oil price we pass through our commodity price changes and go with the 26% increased price target of 30p," it said.
Jefferies lifted its price target on Harbour Energy to 500p from 473p and reiterated its 'buy' rating.
"Harbour Energy stock continues to lag the sector, struggling under the perception of weaker operations given two production guidance revisions since listing in April 2021, and under the stock overhang of expected creditor & PE holder selling, once off lockup.
"However, in our view the market is missing both the operational improvement that is going in 2H21, with Harbour's production and the material leverage to rising commodity prices - in spite of relatively high level off hedging."
At 1240 BST, Tullow shares were up 3.3% at 51.85p, while EnQuest was 6.5% higher at 24.75p and Harbour Energy shares were up 5.2% at 71.46p.